UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

AGRICULTURAL  SCIENCES 

Vol.  2,  No.  1,  pp.  1-46,  pis.  1-12  December  4,  1913 


STUDIES  IN  JUGLANS  I 

STUDY  OF  A  NEW  FORM  OF  JUGLANS  CALIFORNICA 

WATSON 

BY 

ERNEST    B.    BABCOCK 


CONTENTS 

PAGE 

I.  History  and  description. 

First  appearance  and  description  of  the  original  trees  2-5 

General  appearance   - 3 

Leaves  — -       4 

Nuts  4-5 

Recurrence  of  the  new  form  5-6 

Distribution  under  misleading  names  7 

Name  and  botanical  description  7-8 

Comparison  with  the  species  8 

Summary  9 

II.  Origin  of  the  new  form — hypotheses,  observations,  and  experiments. 

Two  discarded  hypotheses  9-11 

First  working  hypothesis — hybridization  11-16 

Results  of  hybridization  experiments  15 

Second  working  hypothesis — teratology  16-20 

Summary  of  evidence  19-20 

Third  working  hypothesis — mutation   21-23 

Summary  of  evidence  23 


2  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

STUDY  OF  A  NEW  FORM  OF  JUGLANS  CALIFORNICA 

WATSON 

I.    History  and  Description 

In  the  autumn  of  1900  D.  C.  Disher,  of  Garden  Grove,  Cali- 
fornia, according  to  his  own  account,  gathered  about  two  thous- 
and nuts  from  a  certain  California  black  walnut  tree  that  grew 
near  Yorba,  in  Santa  Ana  Canon,  but  which  has  since  been 
destroyed.  These  nuts  were  planted  in  the  spring  of  1901  in 
order  to  raise  seedlings  upon  which  to  graft  the  English  walnut 
for  orchard  planting.  Among  the  seedlings  about  twenty 
appeared  from  the  first  to  be  distinct  from  the  rest,  which 
resembled  the  parent  tree.  Of  these  twenty  only  two  trees  remain 
where  they  were  first  transplanted  from  seed-bed  to  nursery 
row,  the  others  having  been  given  away  or  destroyed.  Of  these 
two  only  one  produces  both  male  and  female  flowers  and  bears 
nuts ;  the  other  always  produces  staminate  catkins  in  abundance 
but  no  pistillate  flowers.  For  this  reason  the  first  mentioned 
individual  has  already  been  described1  as  "the  original  fertile 
tree,"  but  it  would  have  been  more  exact  to  have  referred  to  it 
as  Disher 's  fertile  tree,  inasmuch  as  some  of  the  other  original 
specimens  above  mentioned  have  been  located  and  are  known  to 
bear  nuts  also.  The  writer  has  seen  seven  of  these  distributed 
trees,  and  material  from  an  eighth ;  in  leaf  and  bark  characters  as 
well  as  in  general  appearance  they  resemble  Disher 's  trees.  Three 
of  these  are  growing  at  the  experimental  garden  of  N.  B.  Pierce 
in  Santa  Ana,  three  are  located  in  the  town  of  Garden  Grove, 
one  is  on  the  Leffingwell  Ranch  in  East  Whittier,  and  one  is  at 
the  United  States  Plant  Introduction  Gardens  in  Chico,  Cali- 
fornia.   One  of  Pierce's  trees  is  shown  in  plate  13,  figure  16. 

The  discoverer  of  these  trees  wished  to  preserve  them  because 
they  are  so  strikingly  different  in  their  leaf  characters  and  in 
general  habit  from  ordinary  California  black  walnut.  They  pos- 
sess no  special  economic  value,  being  less  robust  than  other  wal- 
nuts and  more  restricted  in  their  range  of  adaptability  to  adverse 


i  Babcock,  E.  B.t  in  Jepson,  The  Silva  of  California,  Mem.  Univ.  Calif. 
II  (1910),  pp.  50-54. 


]913]  Babcock:   New  Form  of  Juglans  3 

soil  conditions.  But  their  structural  characteristics  alone  are 
sufficient  to  excite  the  interest  of  the  student  of  plants,  especially 
of  one  interested  in  problems  of  heredity  and  evolution. 

Perhaps  the  most  interesting  thing  about  these  trees  is  their 
resemblance  to  oak  trees.  In  mass  effect  they  resemble  small- 
leaved  oaks  more  than  walnuts.  This  is  mostly  due  to  the  small 
size  of  the  leaves  and  to  their  color,  which  is  a  darker  or  duller 
shade  of  green  than  that  of  California  black  walnut  leaves.  These 
features,  associated  with  the  fact,  noted  by  Disher,  that  the  parent 
tree  stood  close  beside  a  coast  live  oak  tree  (Quercus  agrifolia 
Nee),  are  sufficient  to  account  for  the  view,  held  by  a  number  of 
persons,  that  this  new  form  originated  through  hybridization 
between  walnut  and  oak. 

As  the  seeds  were  planted  in  1901,  these  trees  are  now 
twelve  years  old.  The  two  retained  by  Mr.  Disher  were 
left  in  the  nursery,  which  was  set  out  to  commercial  varieties 
of  walnut  {Juglans  regia)  later  on  by  the  owner  of  the  farm. 
He  has  allowed  the  trees  to  stand  unmolested,  except  for  trim- 
ming up  low-hanging  branches.  Now  they  have  attained  a  height 
of  twenty-five  feet  and  have  a  spread  of  branches  about  twenty 
feet  in  diameter.  Seen  among  the  broad-leaved  English  walnuts, 
these  two  trees  present  a  distinct  appearance  with  their  many 
slender  branchlets  and  their  sparse  foliage.  In  early  spring  and 
late  autumn  or  early  winter  the  contrast  is  even  greater,  because 
these  trees  and  other  specimens  of  the  new  form  resemble  south- 
ern California  black  walnuts  in  the  brevity  of  their  dormant 
period.  They  leaf  out  very  early  in  spring  and  some  leaves  per- 
sist until  February.  The  English  walnuts,  however,  come  into 
leaf  from  April  to  June,  according  to  the  variety,  and  by  Nov- 
ember are  once  more  leafless. 

Other  distinctive  vegetative  characters  are  well  shown  in  plate 
1,  figure  1.  There  is  a  marked  tendency  to  dichotomous  branch- 
ing. This  is  conspicuous  in  the  left-hand  tree  in  the  picture  and 
is  noticeable  in  the  other  individual.  There  is  also  a  tendency  to 
form  bunches  of  leaves  at  the  ends  of  the  branchlets.  This  is 
apparent  in  both  trees.  The  appearance  of  the  bark  on  the 
trunks  of  Disher 's  original  trees  is  also  distinct  from  that  of 
Juglans  calif ornica.     "While  that  of  the  latter  in  trees  of  the 


4  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

same  age  as  Disher's  is  usually  rough,  the  bark  on  these  trees  is 
rather  smooth. 

The  left-hand  tree  in  plate  1,  figure  1,  always  produces  both 
male  and  female  flowers  and  frequently  bears  abnormal  bisexual 
flowers  also.  But  the  other  tree  produces  only  staminate  cat- 
kins, and  the  photograph  shows  in  what  profusion  they  are  borne. 
A  very  few  pistillate  flowers  have  been  seen  on  this  tree,  but  it 
has  never  been  known  to  bear  fertile  seeds.  That  sterility  in  this 
individual  is  associated  with  greater  vigor  in  wood  production  is 
shown  in  the  above  figure.  The  leaves  on  some  specimens  of 
the  new  form  are  highly  variable.  The  common  type  of  leaf, 
however,  is  one  with  a  terminal  leaflet  one  or  two  inches  long 
and  two  smaller  lateral  leaflets,  as  shown  in  plate  2,  figure  2,  a. 
Sometimes  both  lateral  leaflets  are  missing  and  occasionally  only 
one  is  present,  as  shown  in  plate  2,  figures  2,  b  and  c,  and  in  plate 
3,  figures  4  and  5.  Plate  2,  figure  2,  is  approximately  natural 
size.  In  order  to  appreciate  the  remarkable  difference  in  leaf 
characters  between  the  new  form  and  Juglans  californica  note 
the  leaves  in  plate  7,  figure  11. 

The  frequent  occurrence  of  ascidia  (pitchers)  on  the  leaves 
of  the  Leffingwell  "original"  tree  gives  further  evidence  of  the 
tendency  toward  extreme  variation.  Not  being  aware  that  ascidia 
have  been  reported  previously  in  the  genus  Juglans,  I  give  plate 
2,  figure  3  a  photograph  of  four  leaves  bearing  ascidia  and  one 
normal  leaf. 

The  nuts  borne  on  Disher's  original  fertile  tree  resemble  those 
of  southern  California  black  walnuts  in  external  appearance  of 
the  husk  (cf.  plate  2,  figure  2).  Their  average  size  is  much 
smaller.  The  immature  fruits  are  also  similar,  except  that  many 
of  them  are  ridged  or  grooved  as  in  plate  3,  figure  4,  a,  and 
figure  5,  a,  while  some  depart  widely  in  appearance  from  the 
typical  young  fruit  of  Juglans  californica.  Such  a  specimen  is 
shown  in  plate  3,  figure  5,  b.  The  smooth  area  surrounding  the 
stigma  was  proportionately  large,  and  tapering  arms  extended 
towards  the  base.  Surrounding  the  stigma  were  several  small 
protuberances,  apparently  remnants  of  anthers.  The  occurrence 
of  bisexual  flowers  on  this  tree  has  been  mentioned.  When  the 
dry  husk  is  removed  from  the  mature  nuts  of  this  tree,  they  are 


1913]  Babeock:  New  Form  of  Juglans  5 

seldom  found  to  be  divided  into  nearly  equal  parts  by  a  deep 
suture  but  there  are  sometimes  outer  indications  of  tripartite 
inner  structure.  Such  marks  are  shown  in  plate  4,  figure  6,  I.  The 
occurrence  of  tricotyly  is  frequent  but  many  tripartite  nuts  con- 
tain no  embryos.  Such  a  nut  containing  an  embryo  is  shown  in 
plate  4,  figure  6,  k.  In  dicotyledonous  nuts  from  this  tree  the 
cotyledons  are  reduced,  sometimes  so  much  so  as  to  be  barely 
distinguishable  (cf.  plate  4,  figures  g,  h,  i,  j). 

Recurrence  op  the  New  Form 

In  the  autumn  of  1907,  when  the  writer  first  visited  Garden 
Grove  to  examine  the  original  trees,  he  was  shown  about  a  dozen 
two-year-old  seedlings,  all  of  which  closely  resembled  the  original 
trees.  These  were  found  scattered  through  the  nursery  of  about 
nine  thousand  budded  English  walnut  trees.  The  seedling  roots 
were  grown  from  nuts  collected  in  the  autumn  of  1904,  partly 
from  wild  trees  in  Brea  Canon  and  partly  from  a  row  of  Juglans 
calif ornica  trees  growing  in  Garden  Grove.  The  seeds  had  been 
mixed  so  that  there  was  no  way  of  locating  the  tree  or  trees 
that  gave  rise  to  the  new  form.  Mr.  Disher's  interest  in  the 
unusual  appearance  of  these  seedlings  again  prompted  him  to 
leave  them  unharmed,  so  that  the  writer  was  able  to  secure  a 
fairly  good  photograph  of  one  that  stood  at  the  end  of  a  row 
(cf.  plate  5,  figure  7).  The  contrast  between  this  little  tree  and 
its  luxuriant  neighbors  was  certainly  striking.  The  slender 
branches  and  ovate  leaflets  are  distinctive.  Some  leaves  are  so 
placed  that  the  large  terminal  leaflet  and  two  small  lateral  leaflets 
are  clearly  shown.  One  of  the  seedlings  differed  from  all  the  rest 
in  having  two  pairs  of  lateral  leaflets.  Nearly  all  the  leaves  on 
the  tree  were  of  this  type  (cf.  plate  5,  figure  8).  Since  that  time 
the  writer  has  seen  similar  leaves  on  other  seedlings,  most  of 
whose  leaves  were  three-parted,  as  well  as  leaves  intermediate 
between  the  two.  In  fact,  the  great  amount  of  variation  in  the 
leaves  of  the  several  individuals  which  we  class  as  the  "new 
form"  is  one  of  the  most  interesting  things  connected  with  it 
(cf.  plates  2,  3,  5,  and  11). 

In  1909  William  Tyler,  son-in-law  of  Mr.  Disher,  reported  to 
the  writer  that  he  had  found  a  few  specimens  of  the  aberrant 


6  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

form  among  a  large  number  of  seedlings  of  the  Garden  Grove 
black  walnuts.  This  was  the  third  appearance  of  the  form  in 
question. 

In  the  autumn  of  1910,  the  writer  arranged  to  have  the  nuts 
from  the  various  individual  black  walnut  trees  of  the  row  in 
Garden  Grove  gathered  separately  so  that  they  might  be  planted 
separately  the  following  spring.  The  nuts  were  so  gathered,  but 
unfortunately  became  mixed  while  in  storage.  Thus,  although 
about  thirty  specimens  of  the  new  form  appeared,  they  were  scat- 
tered through  the  nursery  and  could  be  traced  to  no  particular 
tree  or  trees.     This  was  the  fourth  appearance  of  the  new  form. 

In  the  autumn  of  1911  other  parties  secured  many  of  the 
nuts  from  the  Garden  Grove  trees  and  although  a  few  aberrant 
seedlings  appeared  in  Tyler's  seed  beds,  he  was  not  certain  which 
tree  produced  them.  This  makes  the  fifth  appearance  of  the 
form . 

In  1912  the  writer  had  the  product  of  twenty-one  of  the 
trees  in  the  Garden  Grove  row  gathered  separately.  Among  the 
sprouted  seedlings  of  one  tree  six  aberrant  seedlings  have  already 
appeared,  making  the  sixth  appearance.  An  additional  appear- 
ance of  the  new  form  has  been  reported.  In  this  case  a  single 
seedling  appeared  among  those  grown  from  a  mixed  lot  of  south- 
ern California  black  walnut  seeds  from  trees  growing  wild  in 
Santa  Monica  Canon.  The  seeds  were  gathered  in  1910,  so  that 
the  tree  is  now  three  years  old.  It  resembles  Disher's  original 
trees. 

From  the  foregoing  account  it  is  evident  that  the  new  form 
has  originated  in  at  least  three  different  localities.  In  two  of 
these,  Santa  Ana  and  Santa  Monica  canons,  the  trees  were  in  the 
wild  condition  when  the  nuts  were  collected.  The  Garden  Grove 
trees  comprise  a  boundary  line  planting  between  two  farms.  The 
new  form  is  not  reported  to  occur  in  the  wild  and  probably  does 
not  so  occur.  However,  it  would  no  doubt  thrive  in  the  more 
favorable  areas  now  occupied  by  wild  walnuts  in  southern  Cali- 
fornia. Seedlings  of  Disher's  original  trees  have  been  observed 
to  suffer  more  from  excess  of  moisture  than  from  drouth. 

Walnut  breeders  and  nurserymen  have  propagated  the  form 
by   means   of   grafting.     Frank   A.   Leib,   of   San   Jose,   has   a 


1913]  Babcock:   New  Form  of  Juglans  7 

young  tree  grown  from  a  cion  obtained  from  N.  B.  Pierce,  of 
Santa  Ana,  and  grafted  on  a  hybrid  walnut  root  of  the  "royal" 
type.  The  tree  has  made  rather  remarkable  growth.  The  Gar- 
dena  Agricultural  High  School  has  obtained  seeds  of  Disher's 
original  tree  at  Garden  Grove  in  order  to  grow  seedlings  for 
instructional  purposes.  But  there  is  general  confusion  as  to  the 
true  nature  of  the  form  and  it  has  been  distributed  under  mis- 
leading names.  In  view  of  these  facts  it  was  deemed  advisable 
to  record  a  name  indicating  its  natural  relationship  preliminary 
to  the  publication  of  this  paper.2 

Now,  if  this  form  had  been  first  described  from  specimens 
collected  in  the  wild,  there  is  no  doubt  that  it  would  have  been 
named  a  distinct  species.  Without  endeavoring  to  solve  the  prob- 
lem of  its  origin  the  botanist  would  have  felt  justified  in  thus 
naming  it  by  its  absolutely  distinct  foliage  alone.  But  we  do  not 
know  that  it  could  long  exist  under  wild  conditions  and,  as  will 
be  shown  later,  the  seedlings  of  the  original  trees  do  not  come 
uniformly  true  to  type.  Instead  of  so  doing,  usually  some  of 
them  resemble  J.  calif ornica.  Hence,  the  writer  feels  justified  in 
calling  it  a  variety  of  the  species  from  which  it  has  sprung,  no 
matter  by  what  process.  The  following  is  a  description  of 
Disher's  original  fertile  tree  already  published3  with  two  or 
three  minor  changes  based  upon  data  in  the  possession  of  the 
writer. 

NEW  VARIETY 

JUGLANS  CALIFORNICA  var.  QUERCINA  Babcock 

Tree  20  ft.  or  more  high.  Bark  aromatic  and  strongly  walnut- 
scented.  Branchlets  hollow,  chambered  with  pithy  plates.  Twigs,  bud- 
scales,  and  young  leaves  granular-pubescent.  Buds  few-scaled,  axillary 
or  superposed.  Leaves  1  to  3  inches  long,  alternate,  exstipulate,  mostly 
compound  with  three  leaflets;  terminal  leaflet  two  or  three  times  as 
long  as  lateral  leaflets  and  ranging  from  %  to  2  inches  in  length,  in 
form  varying  from  broadly  ovate  through  oval  to  elliptical  or  oblong, 
truncate  or  emarginate  at  the  apex,  margin  serrate  or  almost  entire; 
lateral  leaflets  placed  opposite  or  scattered,  with  petiolules  or  sessile, 
sometimes  one  or  both  lacking;  petiole  equal  to,  shorter  or  longer  than, 
the  terminal  leaflet.     Plant  monoecious,  occasionally  with  hermaphrodite 


-Babcock,    'A   New   Variety   of   Juglans   calif  ornica   Wats."      Science, 
n.  s.,  XXXVIII,  968,  p.  89. 

s  Babcock,  Mem.  Univ.  Calif.  II   (1910),  p.  54. 


8  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

flowers.  Staminate  flowers  in  lateral  catkins  from  wood  of  the  preceding 
year;  calyx  adnate  to  the  inconspicuous  dark-red  bract,  irregular,  con- 
sisting of  three  larger  and  one  or  two  smaller  lobes  and  an  inner  whorl 
of  4  to  6  smaller  distinct  sepals,  one  or  two  of  which  sometimes  show 
stamen  characters;  stamens  sepaloid,  10  to  13,  with  1  to  4  of  the  central 
ones  abortive;  filaments  free,  very  short;  anthers  variable,  the  pollen  sacs 
unequal,  especially  in  the  outermost  stamens,  connective  not  bifid  at  the 
top.  Pistillate  catkins  3  to  6-flowered,  terminating  branchlets  of  the 
same  season's  growth;  calyx  irregularly  4  to  7-lobed,  adherent  to  the 
inferior  1-celled  ovary;  the  latter  often  with  1  or  2  longitudinal  grooves 
or  ridges,  rarely  with  2  or  3  fleshy  bracts  near  the  base,  occasionally 
with  abortive  anthers;  styles  3  or  4,  short,  united  toward  the  base  oi 
free,  stigmatic  along  the  inside,  the  fringed  surfaces  forming  a  rosette. 
Fruit  similar  in  appearance  to  that  of  Juglans  californica  Wats.,  but 
smaller  and  more  variable  as  to  form  and  internal  structure  of  the  nut; 
the  seed  also  much  smaller;  cotyledons  much  reduced,  not  convoluted  (cf. 
plate  1,  figure  1,  plate  2,  figures  2  and  3,  plate  3,  figures  4  and  5,  plate  4, 
figure  6,  g,  h,  i,  j,  k,  I,  plate  5.  figures  7  and  S,  plate  6,  figure  9,  plate  11, 
figures  17  and  18). 


Differences  between  the  New  Form  and  the  Species  Type 


J.  californica 
Leaves,  6  to  13  inches  long,  coin- 
pound  with  11-19  leaflets. 

Terminal  leaflet  shorter  than,  equal 
to,  or  longer  than  the  lateral 
leaflets  and  ranging  from  1% 
to  4  inches  long,  oblong  lance- 
olate,  serrate. 


Staminate  flowers.  Calyx  irregu- 
larly 3  to  6-lobed;  stamens  20 
to  26,  connective  bifid  at  the 
apex. 


Pistillate    flowers. 
styles  2. 


Calyx   4-lobsd; 


Fruit  globose,  %  to  1  inch  in 
diameter;  cotyledons  promin- 
ent, much  convoluted. 


J.  californica  var.  quercina 

Leaves  1  to  3  inches  long,  mostly 
compound  with  3  leaflets,  rarely 
with  5,  sometimes  simple. 

Terminal  leaflet  two  or  three  times 
as  long  as  lateral  leaflets  and 
ranging  from  %  to  2  inches  in 
length,  in  form  varying  from 
broadly  ovate  through  oval  to 
elliptical  or  oblong,  truncate  or 
emaroinate  at  the  apex,  margin 
serrate  or  almost  entire. 

Staminate  flowers.  Calyx  adnate  to 
the  inconspicuous  dark  red 
bract,  irregular  with  3  larger 
and  2  smaller  lobes  and  inner 
whorls  of  4-6  smaller  distinct 
sepals;  stamens  sepaloid,  10  to 
13,  anthers  variable,  connec- 
tive  not  bifid   at   apex. 

Pistillate  flowers.  Calyx  irregular- 
ly 4  to  7-lobed;  styles  3  or  4, 
short,  the  fringed  surfaces 
forming  a  rosette. 

Fruit  smaller  and  more  variable  as 
to  form  and  internal  structure; 
seed  much  smaller,  cotyledons 
much   reduced,  not  convoluted. 


1913]  Babcock:   New  Form  of  Juglans 


SUMMARY 

1.  A  new  form  of  walnut  has  appeared  on  seven  separate  occa- 
sions among  seedlings  of  at  least  three  different  trees  of  Juglans 
calif  ornica  Wats. 

2.  This  form  is  sufficiently  distinct  from  all  other  walnuts  to 
justify  its  recognition  as  a  new  species.  But  in  all  but  one  of  the 
germination  tests  of  seeds  from  the  original  trees,  some  seeds  have 
produced  plants  resembling  the  species  type  in  leaf  characters. 
Moreover,  the  form  is  exceedingly  variable.  These  facts  are  good 
reasons  for  describing  the  new  form  as  a  variety  of  J.  calif  ornica. 


II.    ORIGIN  OF  THE  NEW  FORM— HYPOTHESES, 
OBSERVATIONS  AND  EXPERIMENTS 

In  studying  the  nature  and  origin  of  this  new  form  of  walnut, 
three  working  hypotheses  have  been  retained,  and  two  other 
hypotheses  have  been  eliminated  so  far  as  my  experimental  work 
is  concerned.  The  latter  hypotheses  will  be  discussed  briefly 
before  passing  to  the  fuller  consideration  of  the  working  hy- 
potheses and  the  investigations  connected  therewith. 

One  of  the  first  possibilities  suggested  was  that  the  new  form 
may  be  a  "reversion  to  an  ancestral  type."  The  species  is  long- 
lived  and  stump-sprouts  freely.  A  few  generations  might  extend 
back  to  a  time  when  a  now  extinct  form  existed  in  the  same  area. 
It  is  a  well-known  fact  that  our  present  American  species  inter- 
breed freely  when  growing  near  each  other,  and  also  breed  with 
Juglans  regia  under  similar  conditions.  Hence  it  is  conceivable 
that  such  an  extinct  form  might  have  interbred  with  J.  cali- 
f ornica.  According  to  Mendelian  principles,  some  of  the  progeny 
would  be  heterozygous  for  certain  characters,  which  might  be  the 
distinguishing  characters  of  the  new  form.  Such  heterozygous 
progeny,  under  favorable  conditions,  would  continue  to  produce 
both  parent  forms  and  more  heterozygous  individuals.  It  is 
conceivable,  then,  that  the  few  trees  thus  far  known  to  exist, 
which  are  giving  rise  to  the  new  form,  are  such  heterozygous 
individuals,  and  that  our  new  form  is  really  a  supposed  extinct 


10  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

form,  whose  existence  is  revealed  through  segregation  of  unit 
characters  in  the  gametes  of  the  heterozygous  individuals.  But 
this  conception  was  unsatisfactory  as  a  present  working  hypo- 
thesis, since  it  necessarily  assumes  a  parent  form,  the  existence 
of  which  can  only  be  proved  by  paleontological  records.  So  far 
as  the  writer  has  been  able  to  ascertain,  none  of  the  extinct  species 
of  Juglans  or  Carya  thus  far  described  resemble  the  new  form 
in  number  and  shape  of  leaflets  and  proportionate  size  of  lateral 
and  terminal  leaflets.4  Herbarium  material  of  other  related 
genera  has  also  been  examined  to  see  whether  a  suggestion  of 
the  new  form's  leaf  characters  could  be  found,  but  without  suc- 
cess. However,  until  some  other  hypothesis  is  proved  to  fit  the 
case,  this  one  should  be  reserved  as  having  some  value. 

Another  possibility  is  that  the  new  form  is  a  hybrid  between 
Juglans  calif ornica  and  some  other  species,  such  as  J.  regia  or 
J.  nigra.  This  suggestion  has  not  been  used  as  a  working  hypoth- 
esis because  the  characters  of  hybrids  between  these  two  species 
and  J.  calif  ornica  are  already  known.  It  is  generally  understood 
that  plants  of  the  F1  generation  of  both  these  crosses  reveal 
the  partial  dominance  of  J.  nigra  or  J.  regia  as  the  case  may  be.5 
They  always  have  larger  leaves  than  those  of  J.  calif  ornica, 
whereas  our  new  form  is  characterized  by  its  small  leaves.  It 
is  hardly  conceivable,  then,  that  the  new  form  is  the  direct  result 
of  such  a  cross,  nor  even  that  the  wild  trees  from  which  our  new 
form  springs  could  belong  to  the  F1  or  a  later  generation  from 
such  a  cross  and  thus  produce  the  new  form  among  the  extreme 
variations  that  sometimes  occur  among  the  younger  generations 
of  hybrids  between  species.  For  our  new  form  is  the  only 
extreme  variation  which  has  been  reported  among  the  many 
thousands  of  J.  calif  ornica  seedlings  that  are  grown  annually  in 
California.  Moreover,  <7.  regia  has  been  cultivated  in  southern 
California  for  less  than  fifty  years,  while  only  a  few  cultivated 
trees  of  J.  nigra  occur,  and  these  also  came  with  the  introduction 
of  commercial  walnut  growing.     Other  known  species  of  Juglans 


*  Dr.  W.  A.  Berry,  in  a  letter  to  the  writer,  expressed  the  following 
opinion:  "I  suspect  if  a  paleobotanist  had  come  across  such  a  form,  and 
I  know  of  none  such,  he  would  have  thought  of  the  Anacardiaceae  rather 
than  Juglans. ' ' 

s  Smith,  R.  E.,  "Walnut  Culture  in  California,"  Univ.  Calif.  Agr.  Exp. 
Sta.  Bull.  231,  pp.  157-170. 


1913]  Babcock:   New  Form  of  Juglans  11 

are  also  sufficiently  distinct  from  J.  californica  so  that  hybrid 
offspring  of  the  F1  generation  would  hardly  resemble  our  new 
form.  Exceptions  to  this  would  be  J.  rupestris  and  J.  major, 
the  Texan  and  Arizonan  species,  which  resemble  J.  californica 
rather  closely,  and  on  this  account  the  possibility  of  our  new  form 
being  an  F1  hybrid  between  either  of  these  species  and  J.  califor- 
nica is  even  less  likely.  Hence,  while  it  is  very  desirable  that  a 
systematic  study  of  hybridization  among  all  species  of  Juglans 
should  be  made,  because  of  its  botanical,  genetic  and  horticultural 
interest,  the  writer  does  not  consider  it  likely  that  the  new  form 
is  a  hybrid  between  J.  californica  and  any  other  known  member 
of  the  genus.  By  analogy  we  may  eliminate  all  other  members  of 
the  family  Juglandaceae  from  similar  participation  in  the  origin 
of  the  new  form. 

Turning  next  to  the  three  hypotheses  which  serve  as  a  basis 
for  the  investigation  now  in  progress,  it  would  seem  that  sufficient 
work  along  any  one  of  these  lines  might  lead  to  a  solution  of  the 
problem.  They  will  be  discussed  in  the  order  in  which  they 
were  originally  taken  up  by  the  writer.     They  are  as  follows : 

(1)  The  new  form  may  be  a  natural  hybrid  between  Juglans 
californica  Wats.,  and  Quercus  agrifolia  Nee,  or  some  other  oak. 

(2)  The  new  form  may  originate  in  certain  teratological 
flowers  that  have  been  discovered  on  certain  Juglans  californica 
trees. 

(3)  The  new  form  may  be  the  result  of  mutations  in  certain 
male  or  female  flowers  (or  both)  of  certain  Juglans  californica 
trees. 

First  Hypothesis 

Let  us  consider  first  the  possibility  of  origin  through  hybrid- 
ization between  walnut  and  oak.  The  original  trees  were  first 
shown  to  the  writer  as  "crosses  between  a  walnut  and  an  oak." 
They  were  briefly  described  by  him  under  the  title  ' '  The  Walnut- 
Oak  Hybrids,"  in  Jepson's  The  Silva  of  California  (pp.  50-54). 
In  1907,  N.  B.  Pierce  verbally  expressed  to  the  writer  his  opinion 
that  the  new  form  is  a  hybrid.  Since  the  conception  of  hybrid 
origin  was  entertained  by  various  persons,  it  seemed  wise  to 
investigate  the  possibility,  not  only  of  the  occurrence  of  natural 


12 


University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 


hybrids,  but  also  of  producing  such  hybrids  artificially.  From 
the  descriptions  of  the  two  families  it  is  evident  that  they  are 
rather  closely  similar.  Following  is  a  table  of  comparison"  of 
the  reproductive  organs  in  Juglans  and  Quercus : 


Juglans 

Plants  monoecius. 

Staminate  flowers  on  lateral  pen- 
dulous catkins  on  last  season  's 
wood;  calyx  irregularly  3  to 
6-lobed;  stamens  numerous. 

Pistillate  flowers  solitary  or  few  in 
a  short  terminal  spike;  calyx 
4-lobed,  adherent  to  the  1- 
celled  inferior  ovarv;  styles  2. 


Fruit  a  1-eelled,  incompletely  par- 
titioned nut,  1-seeded,  the  seed 
so  lobed  as  to  fit  the  irregulari- 
ties of  the  cavity,  exterior  of 
nut  covered  with  green  and 
fleshy  or  at  length  dry  and 
brown    husk. 


Quercus 

Plants  monoecius. 

Staminate  flowers  on  pendulous  (ex- 
cept in  one  species)  catkins 
from  buds  of  the  previous  sea- 
son; calyx  parted  into  several 
lobes;  stamens  4  to  12. 

Pistillate  flower  1  in  an  involucre; 
involucres  1  or  2  in  the  upper 
axils  of  the  season's  shoot: 
calyx  adherent  to  the  3-celled, 
6-ovuled  ovary;  ovary  with  3 
to  5  styles  or  stigmas. 

Fruit  a  1-celled,  1-seeded  nut,  only 
1  ovule  maturing;  seed  with 
thick,  fleshy  cotyledons;  the 
nut  set  in  a  scaly  cup. 


From  the  above  table  it  is  evident  that  in  gross  structure 
of  flowers  the  two  genera  are  closely  similar.  Of  course,  there 
is  always  the  possibility  or  likelihood  that  some  feature  in  the 
minute  structure  of  the  pistillate  flowers  or  in  the  physiology  of 
fertilization  may  absolutely  prevent  hybridization  between  any 
and  all  species  of  the  two  genera.  The  writer  has  not  yet  been 
able  to  engage  in  the  cytological  study  necessary  to  confirm  or 
deny  this  possibility. 

The  first  effort  made  was  to  search  for  chance  natural  hybrids 
in  the  wild.  In  1907  about  four  thousand  nuts  of  Juglans  cali- 
fornica  were  gathered  in  Brea  Caiion.  They  were  taken  from 
trees  standing  close  to  coast  live  oaks.  As  they  were  planted  late 
in  the  spring  they  were  slow  in  germinating  and  cutworms 
destroyed  many  of  them,  but  among  two  hundred  that  grew 
during  the  summer  of  1908,  no  aberrant  forms  appeared.  No 
further  efforts  in  this  direction  were  made,  as  the  possibilities 
of  success  were  considered  too  remote  to  warrant  the  expense  of 
collecting  and  growing. 


8  Based  on  descriptions  of  the  genera  in  Jepson  's  The  Silva  of  Cali 
fornia. 


1913] 


Babcock:   New  Form  of  Juglans 


13 


In  undertaking  cross-pollination  experiments  it  was  reasoned 
that  the  failure  of  a  large  number  of  careful  efforts  to  secure 
such  a  hybrid  would  discredit  this  hypothesis,  while  the  produc- 
tion of  one  such  hybrid  artificially  would  tend  to  strengthen  it. 
During  the  first  year's  work  the  only  oak  experimented  with  was 
the  coast  live  oak,  Quercus  agrifolia,  but  in  succeeding  years  one 
or  more  other  species  were  included  in  the  trials.  The  female 
flowers  used  were  all  on  J.  calif omica  trees  in  1908,  but  since  that 
year  an  effort  has  been  made  (yet  without  success)  to  secure 
reciprocal  crosses. 


Experiments  in  1908,  1909,  and  1910 

Two  indigenous  walnut  trees  were  selected.  They  were 
located,  one  at  the  rear  and  the  other  at  the  front  of  a  large  city 
lot  in  the  suburbs  of  Los  Angeles.  Through  the  courtesy  of  the 
residents,  they  were  protected  from  interference  during  the 
critical  stage  of  the  work.  They  will  be  designated  as  Tree  I 
and  Tree  II. 

Manila  paper  bags  were  placed  over  the  pistillate  catkins 
almost  as  soon  as  they  appeared  and  before  pollen  was  being  shed 
by  the  staminate  catkins.     Oak  pollen  was  collected  in  homeo- 


SUMMARY    FOR    1908 

Tree  I 


bource  of 
pollen 

Q.  agrifolia  .... 

Number  of 
pistillate 
catkins 

pollinated 

23 

Number  of 

catkins 

on  which 

nuts  formed 

14 

Number  of 
nuts  produced 

27 

Nut 

gem 

in 

s  that 
linated 
1909 

26 

Trees 

growing 

in  1913 

24 

Freak   S. 

19 

8 

13 

13 

12 

Checks  

8 

0 
Tree 

0 
II 

0 

0 

Q.  agrifolia  .... 

17 

16 

37 

33 

32 

Cheeks  

5 

1 

2 

2 

2 

pathic  vials  and  applied  with  camel's-hair  brushes.  In  1908  no 
pollen  was  being  shed  on  Tree  I,  even  at  the  time  of  pollination. 
On  Tree  II  pollen  was  being  shed  but  care  was  used  not  to  expose 


14  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

the  pistillate  flowers  when  pollinating  them.  The  only  other 
source  of  pollen  in  1908  was  Disher's  original  sterile  tree,  which 
is  referred  to  below  as  Freak  S.  In  the  following  table  "checks" 
are  bags  that  were  left  in  place  at  time  of  pollination  and  allowed 
to  remain  for  several  weeks,  in  order  to  learn  whether  nuts  would 
develop.  The  trees  referred  to  as  growing  in  1913  are  located 
on  the  campus  of  the  University  of  California. 

In  1909.  the  walnuts  were  very  late  in  blooming  and  conditions 
were  so  adverse  that  no  nuts  whatever  were  produced  as  a  result 
of  pollinating  thirty-four  different  catkins  (about  sixty  flowers). 

In  1910  conditions  were  favorable  and  very  promising.  In 
May,  1910,  there  were  151  nuts  developing  as  a  result  of  pollin- 
ating 79  pistillate  catkins  with  Quercus  agri folia  pollen,  and  29 
nuts  as  a  result  of  pollinating  16  pistillate  catkins  with  Q.  engel- 
manni  pollen.  But  through  a  miscalculation  on  the  part  of  an 
assistant  regarding  the  proper  time  to  secure  the  nuts  before  they 
dropped  from  the  trees,  the  entire  lot  was  lost.  However,  this 
assistant,  S.  E.  Goodall,  made  similar  experiments  at  his  home 
near  Chatsworth,  using  pollen  from  Q.  agrifolia  and  Q.  lobata. 
The  oak-pollinated  nuts  were  protected  and  saved,  and  as  a 
result  there  are  growing  on  the  campus  of  the  University  of  Cali- 
fornia eight  young  trees  from  Q.  agrifolia  pollinations  and  four 
from  Q.  lobata  pollinations. 


Experiments  in  1911 

The  trees  used  are  located  on  F.  Goodall 's  ranch  near  Owens- 
mouth,  Los  Angeles  County.  Three  different  trees  were  used. 
They  will  be  designated  by  the  letters  A,  B,  and  C.  Coffee  bags, 
having  the  outer  layer  of  oiled  paper,  were  used  to  cover  pistillate 
flowers.  An  effort  was  also  made  to  secure  reciprocal  hybrids. 
One  tree  of  Quercus  lobata  was  found  which  was  shedding  but 
little  pollen  and  which  was  somewhat  removed  from  others  of  its 
kind.  Bags  were  placed  over  seven  shoots  of  the  season's  growth, 
thus  covering  forty  to  fifty  pistillate  flowers,  after  first  having 
pollinated  them  with  J.  calif  omica  pollen.  Three  weeks  later 
the  bags  were  removed  and  some  flowers  seemed  likely  to  develop 
further,  although  some  were  moldy.    On  July  21  all  had  dropped. 


abcock:   New  Form  o 

f  Juglans 

IE 

Summary  for 

1911 

Tree  A 

Number  of  pistillate 
catkins  pollinated 

20 

Number  of  nuts 

produced 

9 

Nuts  germinated 
June  1,  1912 

0 

20 

9 

0 

12 

4 

2 

1  1 

4 

0 

Tree  B 
24 

18 

15 

13 

10 

7 

1913] 


Source  of 
pollen 

Q.  agrifolia  

Q.  lobata  

Q.  dumosa  

Checks  

Q.  agrifolia  

Cheeks  

Trees  B  and  C" 
Q.  lobata  44  29  22 

Results  of  Hybridization  Expt  riments 

From  the  1908  pollinations  with  Quercus  agrifolia  upon  Jug- 
lans calif omica  there  are  now  48  four-year-old  seedlings.  Cions 
from  most  of  these  have  been  grafted  this  spring  upon  large 
English  walnuts  in  order  to  hasten  fruiting.  It  is  planned  to 
protect  these  grafts  at  the  blooming  period  so  as  to  secure  self- 
fertilization  and  thus  make  possible  the  "  breaking-up "  which 
may  occur  in  the  F2  generation  if  they  are  really  hybrids. 

From  the  1910  experiments  (made  by  Goodall)  there  are  eight 
seedlings  from  the  Q.  agrifolia  pollinations  and  four  from  Q. 
lobata  pollinations.    Grafts  may  be  made  from  these  next  year. 

From  the  1911  experiments  there  are  14  seedlings  from  the 
Q.  agrifolia  pollinations,  20  from  the  Q.  lobata,  and  2  from  the 
Q.  dumosa  crosses. 

The  seedlings  obtained  from  all  oak  pollinations  resemble  ./. 
calif  omica  in  leaf  characters  and  habit  of  growth.  This  does  not 
necessarily  mean  that  these  seedlings  are  not  true  hybrids.  It 
has  been  demonstrated  that  certain  species-hybrids  are  goneoclinic 
to  the  female  parent  in  the  F1  generation.8  It  is  in  the  hope  of 
showing  that  these  seedlings  are  hybrids  by  the  appearance  of 
oak  characters  in  plants  of  the  F2  generation  that  the  seedlings 
are  being  propagated  to  secure  early  fruiting.9 


7  While  in  storage  the  Q.  lobata  nuts  from  Trees  B  and  C  became 
mixed,  but  24  of  the  29  came  from  Tree  C. 

s  Keeble,  F.,  The  Gardener's  Chronicle,  vol.  52,  no.  1355,  p.  457. 

:)  Since  writing  the  above  it  has  been  found  that  most  of  the  seedlings 
from  the  1908  crosses  bloomed  this  spring  (1913).  Hence  it  was  possible 
to  secure  self-pollination  on  the  seedlings  themselves  at  an  earlier  date 
than  was  anticipated. 


16  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

In  1908  the  check  results  were  much  more  satisfactory  than 
in  1911.  Various  factors  may  have  influenced  these  results,  hut 
the  writer  is  inclined  to  think  that  the  comparative  isolation  of 
the  Los  Angeles  trees  made  them  more  satisfactory  subjects  for 
experimentation.  From  the  1911  results  we  find  nearly  as  high 
a  percentage  of  nuts  in  check  bags  as  in  pollinated  bags  from 
Tree  A  and  a  higher  percentage  from  Tree  B.  The  production 
of  nuts  in  the  check  bags  raises  the  question  of  the  possibility  of 
apogamic  development  of  seed  in  Juglans  calif  arnica,  and  throws 
a  shade  of  doubt  upon  the  supposed  hybrid  seedlings  that  have 
been  obtained  from  oak  pollinations.  In  this  connection  more 
experimental  work  should  be  done  in  preventing  natural  pollina- 
tion on  a  large  scale. 

For  the  present  the  writer  is  inclined  to  think  that  one  of 
the  other  two  hypotheses  is  much  more  likely  to  reveal  the  origin 
of  our  new  form.  Dr.  Cannon,  of  the  Desert  Laboratory,  Car- 
negie Institution  of  Washington,  who  is  an  authority  on  plant 
hairs,  informs  me  that  he  finds  no  evidence  of  oak  characters 
in  the  hairs  of  Disher's  original  trees. 

Second  Hypothesis 

Let  us  consider  next  the  possibility  that  the  new  form  may 
originate  in  certain  teratological  flowers  on  certain  Juglans  cali- 
fornica  trees.  It  is  necessary  to  give  here  a  brief  account  of 
the  discovery  of  these  abnormal  flowers  and  to  state  the  reasons 
for  considering  them  as  a  possible  source  of  the  new  form.  In 
order  to  emphasize  the  teratological  features  about  to  be  described, 
it  may  be  well  to  consider  first  the  characteristics  of  normal  fruits 
and  flowers.  Normal  flowers  are  shown  in  plate  6,  figure  10. 
Normal  leaves  and  fruits  are  shown  in  plate  7,  figure  11. 

The  normal  blooming  period  of  most  wild  black  walnut  trees 
in  southern  California  is  in  April.  As  the  staminate  catkins  are 
produced  upon  the  wood  of  the  previous  season's  growth,  their 
gradual  increase  in  size  may  be  observed  at  any  time  during  late 
winter  or  spring.  During  March  they  lengthen  noticeably. 
About  April  first  the  pistillate  catkins  appear,  terminating  the 
first  new  growth  of  the  season.  They  are  one  or  two  inches 
long  and  bear  one  to  five  flowers,  so  that,  when  the  fruits  mature. 


1913]  Babcock:   New  Form  of  Juglans  17 

they  often  hang-  in  clusters  (cf.  plate  7,  figure  11).  Normal  pistil- 
late flowers  are  bisymmetrieal.  Normal  staminate  catkins  are 
two  to  four  inches  long,  pendulous,  and  bear  an  indefinite  num- 
ber of  flowers  (cf.  plate  6,  figure  10). 

Many  trees  throw  out  lateral  branchlets  from  the  first  growth 
of  the  season.  It  is  usually  during  this  second  period  of  growth, 
in  May  or  early  June,  that  teratological  flowers  and  leaves  appear 
on  certain  trees.  (It  should  be  noted  here  that  abnormal  female 
flowers  have  been  observed  by  the  writer  during  the  normal 
blooming  period  of  two  or  three  trees.  A  note  on  such  specimens 
with  illustrations  appears  in  Jepson's  The  Silva  of  California,  pp. 
55,  56.  So  far  as  is  known  these  flowers  never  produce  fruits 
containing  viable  seeds.)  The  late  or  second-growth  abnormal 
flowers  are  usually  produced  upon  catkins  that  resemble  normal 
staminate  catkins  in  number  and  arrangement  of  flowers.  But 
the  flowers  are  either  pistillate  or  bisexual,  often  both  occurring 
on  the  same  catkin.  Only  a  few  staminate  flowers  have  been 
observed  among  these  late  blooms,  and  these  were  on  catkins 
which  were  entirely  staminate.  One  tree  was  observed  on  May 
2!),  1909.  on  which  nearly  all  the  late  or  second-growth  catkins 
were  staminate,  but  the  flowers  were  dropping  instead  of  devel- 
oping to  maturity.  Most  late-appearing  catkins  occur  on  the 
second-growth,  lateral  branchlets,  one  catkin  in  the  axil  of  a  leaf. 
but  they  sometimes  develop  alongside  the  normal,  terminal,  pis- 
tillate catkin,  as  shown  in  plate  8,  figure  12.  In  Brea  Canon 
(Puente  Hills)  a  hundred  or  more  wild  trees  were  examined 
during  the  season  of  1909,  and,  while  abnormal  flowers  and  fruits 
were  not  of  general  occurrence,  they  were  found  to  be  verj 
frequent. 

The  most  striking  characteristic  of  the  pistillate  and  bisexual 
flowers  is  their  form.  They  are  asymmetrical,  being  flattened 
more  or  less  on  the  side  adjacent  to  the  axis  of  the  catkin.  Along 
with  this  flattening  there  is  often  a  depression  in  the  surface  of 
the  ovary,  usually  extending  from  the  styles  to  the  base  of  the 
ovary  or  only  part  way,  and  of  varying  width  (cf.  plate  8, 
figure  12). 

When  teratological  flowers  develop  into  fruits,  the  asymmetri- 
cal form  and  principal  surface  markings  are  retained.    Over  fifty 


18  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

abnormal  fruits,  with  their  husks  dry  and  brown  but  in  most 
cases  uninjured,  were  picked  up  by  the  writer  beneath  one  of 
the  several  trees  upon  which  such  fruits  have  been  known  to 
mature.  But  most  of  these  trees  produced  only  a  few  such  fruits. 
Mature  abnormal  fruits  are  easily  assorted  into  two  or  three  lots 
according  to  their  external  markings.  Very  few  differ  notably 
from  the  two  classes  illustrated  in  plate  9,  figure  13.  However, 
in  each  class  there  are  greater  extremes  of  variation  than  are  here 
shown.  The  series  a,  b,  c  has  been  designated  "Type  X"  and 
the  other  series,  "Type  Y."  In  a,  b,  c,  d,  e,  the  fruits  appear  as 
when  picked  up;  a,  b,  c,  are  seen  in  longitudinal  plane,  while 
d  and  e  are  seen  from  above;  in  a',  b' ,  c',  d' ,  e' ,  the  dry  husk 
has  been  entirely  removed  from  the  woody  shell  of  the  nut.  These 
nuts  are  from  fruits  which  resemble  a,  b,  c,  d,  and  e  so  closely  as 
to  be  practically  identical.  While  a',  c' ,  e'  are  seen  from  above, 
b'  and  d'  are  shown  in  longitudinal  plane.  The  nuts  a",  b" ,  c", 
d",  e"  are  practically  identical  with  a' ,  b' ,  c',  d'  and  e' .  They 
were  sectioned  transversely  and  placed  in  relatively  the  same  posi- 
tions as  a',  b',  c',  d'  and  e'  respectively,  the  basal  portion  of  the 
nut  being  placed  in  the  upper  of  the  two  rows  in  each  case.  To 
me,  the  most  striking  abnormality  shown  in  this  picture  is  tin; 
unequal  reduction  of  the  cotyledons  in  all  except  e" . 

Two  culture  tests  of  abnormal  nuts  selected  to  these  types 
have  been  made  in  1910  and  1911.  There  is  considerable  varia- 
tion among  the  seedlings  grown  from  each  type,  but  no  general 
differentiating  character  could  be  found  among  all  the  seedlings 
from  the  two  types  of  nuts.  These  tests  were  subsidiary  to  the 
general  trials  of  abnormal  nuts  conducted  during  the  same  years 
in  order  to  ascertain  whether  the  new  form  originates  from  such 
nuts.  Among  sixty-eight  seedlings  growing  not  one  has  shown 
the  slightest  indication  of  the  leaf  characters  of  the  new  form. 
In  1910  trials  one  seedling  appeared  that  had  three-parted  scale- 
like leaves,  but  it  died  before  it  was  three  inches  high.  The  leaves 
did  not  resemble  those  of  the  new  form. 

On  otherwise  normal  Juglans  califomica  trees,  abnormal 
leaves  have  been  observed  in  two  situations — near  the  base  of 
second-growth  lateral  branchlets  and,  occasionally,  associated  with 
the  abnormal  catkins  already  described.     Abnormal  leaves,  from 


1913]  Babcock:   New  Form  of  Juglans  10 

second-growth  lateral  branchlets  on  trees  bearing  abnormal 
flowers,  and  leaves  associated  with  abnormal  catkins  are  shown 
in  plate  9,  figure  14.  Some  of  these  leaves  resemble  somewhat 
the  typical  leaves  of  the  new  form  and,  at  the  same  time  the  leaves 
shown  here  were  collected,  one  second-growth  lateral  branchlet 
was  found  that  bore  a  leaf  very  similar  to  the  typical  leaf  of  the 
new  form  (cf.  plate  10,  figure  15,  a). 

We  may  now  summarize  the  phenomena  observed  in  connec- 
tion with  the  occurrence  of  teratology  in  Juglans  calif  arnica  and 
add  some  considerations  with  respect  to  the  possible  origin  of  the 
new  variety.  Abnormal  flowers,  fruits  and  leaves  are  of  frequent 
occurrence  on  indigenous  trees.  They  usually  occur  later  in  the 
growing  season  than  the  normal  blooming  period,  on  secondary, 
lateral  branchlets,  or  in  the  case  of  abnormal  catkins,  sometimes 
as  secondary  catkins  terminating  the  first  growth  of  the  season. 
The  fruits  produced  by  abnormal  flowers  retain  the  characters  of 
asymmetry  and  irregularity  of  surface.  Their  average  size  is 
only  about  half  that  of  normal  fruits. 

Only  a  small  percentage  of  the  abnormal  fruits  collected  by 
the  writer  contained  viable  seeds.  Among  all  the  seedlings  which 
have  been  grown  from  abnormal  nuts,  not  one  shows  a  trace  of 
the  leaf  characters  of  the  new  form.  On  the  other  hand,  in  con- 
nection with  the  fourth  recurrence  of  the  new  form  at  Garden 
Grove  in  the  spring  of  1911,  the  writer  was  able  to  ascertain 
definitely  that  some  of  the  seedlings  of  the  new  form  grew  from 
nuts  of  normal  size  and  shape.  These  facts  indicate  that  the  new 
form  does  not  originate  from  teratological  fruits.  However,  we 
must  concede  the  possibility  of  the  original  trees  having  so 
originated.  More  of  these  abnormal  nuts  should  be  collected  and 
the  seeds  tested. 

The  reasons  for  thinking  that  the  new  variety  may  have  orig- 
inated from  teratological  fruits  may  be  concisely  stated  as  fol- 
lows : 

1.  There  is  more  or  less  similarity  between  the  abnormal 
leaves,  found  on  secondary  branchlets  or  associated  with  abnor- 
mal catkins,  and  the  leaves  of  the  new  form. 

2.  Abnormal  flowers  and  fruits  are  frequently  found  during 
the  normal  blooming  period  on  some  of  the  original  trees  of  the1 


I'd  University  of  California  Publications  in  Agricultural  Sciences    |  Vol.  :_' 

new  form  and  in  considerable  variety,  especially  the  flowers, 
many  of  which  do  not  mature  into  fruits.  Bisexual  flowers  are 
rather  frequent  and.  whether  bisexual  or  not,  the  flowers  often 
have  peculiar  external  markings  on  the  ovary  resembling  those 
already  noted  in  the  teratological  flowers  above  described. 

3.  Late  flowers,  i.e..  abnormal  catkins  on  second-growth  wood, 
have  been  observed  on  four  of  the  seven  original  trees  of  the 
new  form  examined  by  the  writer.  The  other  three  trees  seldom 
bear  any  flowers.  Specimens  of  these  abnormal  calkins  collected 
from  the  Leffingwell  original  tree  in  1909  are  shown  in  plate  11. 
figure  17.  Prom  the  size  of  the  normal  young  fruit  shown  at  a, 
the  difference  in  time  beiween  the  normal  blooming  period  and 
the  appearance  of  these  abnormal  calkins  may  be  inferred.  The 
flowers  on  these  abnormal  catkins  are  very  small  and  abortive  and 
the  leaves,  shown  at  a.  b.  r.  and  d.  resemble  the  leaves  shown  at 
d,  e,  and  /'  in  plate  9.  figure  14.  which  were  associated  with 
abnormal  catkins  on  indigenous  Juglans  calif ornica  trees. 

4.  There  is  no  apparenl  obstacle  to  the  natural  pollination  of 
the  late-appearing  teratological  flowers,  as  some  of  them  are 
bisexual  and  free  pollen  has  been  observed  in  these  bisexual 
flowers.  Also  a  few  late  staminate  catkins  have  been  found. 
Moreover,  there  is  wide  variation  in  the  normal  blooming  period 
among  individual,  indigenous  I  rei  s.  The  young  fruits  of  different 
trees  have  been  observed  to  vary  in  size  from  nearly  full-grown 
down  to  five-eighths  of  an  inch  in  diameter.  It  is  possible,  then, 
that  the  normal  pollen  produced  on  late  trees  mighl  fertilize  alt- 
normal  flowers  on  early  blooming  individuals.  However,  in  the 
lest  for  apogamic  development  of  normal  fruits  it  would  be 
interesting  to  test  these  teratological  flowers  also. 

The  reasons  for  not  thinking  the  new  variety  originated  in 
late  teratological  flowers  are  as  follows: 

1.  Sixty-eighl  seedlings  have  been  grown  from  teratological 
nuts  and  none  have  resembled  the  new  form. 

2.  The  new  form  is  known  to  have  been  produced  by  nuts 
of  normal  size  and  shape. 

From  the  data  at  hand,  the  writer  is  inclined  to  consider  the 
second  hypothesis  as  approaching  more  nearly  to  the  truth  than 
the  first,  but  thus  far  direct  evidence  fails  to  support  it. 


L913]  Bdbcock:  New  Form  of  Juglans  21 

Third  Hypothesis 

The  possibility  that  the  original  trees  of  the  new  form  are 
mutants  has  been  recognized  from  the  first.  If  it  can  be  shown 
that  the  recurrence  of  this  form  among  seedlings  of  Juglans  cali- 
fornica  trees  is  due  to  repeated  mutations  in  certain  individuals, 
this  would  be  good  evidence  that  the  original  trees  were  similarly 
produced.  The  repetition  of  mutations  is  not  contrary  to  experi- 
ence but  rather  is  characterstic  of  species  known  to  be  in  a 
mutating  period.  It  is  generally  admitted  that  plants  exhibiting 
the  evidence  of  being  in  a  mutating  period  are  rare.  "Hugo  de 
Vries  admet  l'hypothese  d'une  mutabilite  periodique  et  rare" 
(Blaringhem).  Among  the  plants  reported  as  being  in  such  an 
abnormal  condition,  the  number  of  trees  is  very  small.  Hence 
the  phenomena  connected  with  the  occurrence  and  recurrence  of 
this  new  form  of  walnut  gather  increased  interest  as  soon  as 
the  hypothesis  of  origin  by  mutation  is  considered. 

The  chief  obstacle  to  adequate  investigation  based  on  the 
hypothesis  has  been  the  difficulty  in  locating  a  single  tree  of 
Juglans  californica  from  whose  seeds  the  new  form  is  known  to 
grow.  With  such  a  tree  located  under  conditions  favorable  to 
experimental  work,  a  careful  study  of  its  vegetative  and  repro- 
ductive parts  can  be  made  and  pollination  may  be  controlled. 
After  several  years  of  searching  such  a  tree  has  now  been  located. 
It  is  a  certain  tree  in  the  Garden  Grove  row  of  black  walnuts1" 
from  which  nuts  have  been  gathered  by  nurserymen,  who  have 
found  seedlings  of  the  quercina  type  during  a  period  of  several 
consecutive  years. 

In  1912  I  had  the  nuts  from  twenty-one  of  the  trees  in  this 
row  gathered  separately,  labeled  with  numbers  corresponding  to 
numbers  attached  to  the  trees,  and  shipped  to  Berkeley.  These 
were  soaked,  planted  in  sand  in  fiats,  properly  Labeled  and  placed 
under  the  benches  of  a  glass  house,  in  February,  1913.  Two 
months  later,  six  quercina  seedlings  were  found  in  the  fiats  from 
tree  No.  16.  There  were  275  seedlings  in  all.  Thus  slightly  over 
two  per  cent  of  the  seedlings  secured  from  the  11)12  crop  of  this 
tree  appear  to  be  mutants.  Plate  11,  figure  18,  shows  one  of 
these  seedlings  and  one  normal  seedling  from  tree  No.  16.     Plate 


10  Cf.  Recurrence  of  the  New  Form,  j>.  5. 


22  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

12,  figure  19,  is  from  a  photograph  of  tree  No.  16  taken  in  April. 
1913.  About  four  hundred  twigs  on  this  tree  likely  to  bear  nuts 
have  been  covered  so  as  to  insure  self-pollination.  In  this  way 
it  is  hoped  to  locate  the  twig  or  twigs  producing  mutants. 

The  data  at  hand  indicate  that  the  new  form  is  not  a  typical 
mutation  from  the  seed  in  the  usual  meaning  of  that  expression. 
All  but  one  of  the  tests  of  the  seeds  from  the  original  trees  have 
revealed  a  partial  reversion  to  the  species  type  in  the  second 
generation  (counting  Disher's  original  trees  as  the  first  genera- 
tion). Now,  one  of  the  generally  accepted  distinguishing  char- 
acteristics of  a  mutant  is  that  it  breeds  true  from  the  first,  but 
here  is  a  remarkably  distinct  form  which  does  not  breed  true.  Of 
course,  this  should  not  exclude  the  possibility  of  origin  by  muta- 
tion of  an  "eversportin"'  variety."  It  is  quite  possible  thai 
quercina  is  an  eversporting  variety  and.  if  so.  it  may  still  have 
originated  without  an  antecedent  hybridization,  but  would  then 
never  breed  true.11  However,  it  does  not  appear  to  the  writer 
that  the  term  "eversporting  variety"  as  used  by  De  Vries  is 
applicable  to  this  form.  De  Vries  classes  as  eversporting  varieties 
such  inconstant  forms  as  striped  flowers,  live-leaved  clovers,  and 
polycephalic  poppies.  But  in  this  new  walnut,  we  have  a  form 
which  is  distinct  in  most  of  its  characters  from  the  parent  form 
and  which  breeds  true  in  a  portion  of  its  offspring,  the  remaining 
portion  showing  complete  resemblance  to  the  parent  form. 

It  has  been  suggested  by  Professor  II.  B.  Torrev  that  muta- 
tions may  occur  in  the  gametes  of  one  sex  while  the  gametes  of 
the  other  sex  are  normal  and,  hence,  that  the  new  form  appeal's 
among  first  generation  seedlings,  but  fails  to  breed  true  in  the 
second  generation. 

Some  doubts  as  to  Professor  Torrey's  suggestion  arise  when 
we  consider  the  results  of  a  pollination  experiment  which  the 
writer  made  in  1908.  Pollen  from  Disher's  original  non-fruiting 
tree  was  placed  upon  pistillate  flowers  of  Tree  I,  referred  to  in 
the  discussion  of  the  first  hypothesis.  All  of  the  eleven  seedlings 
growing  from  this  cross  resemble  Jittjla/is  californica.  On  the 
basis  of  Professor  Torrey's  suggestion,  this  would  be  explained 


11  Dr.  George  H.  Shull  kindly  suggested  the  explanation   on   the  basis 
that  quercina  is  an  eversporting  variety. 


L913]  Babcook:   New  Form  of  Juglans  23 

by  assuming  that  the  pollen  grains  engaged  in  fertilization  bore 
-/.  call) "ornica  characters  as  a  result  of  segregation  in  the  reduc- 
tion divisions.  But  it  is  as  reasonable  to  explain  these  results 
by  assuming  that  the  ovnle-borne  characters  of  J .  calif  ornica 
are  dominant  or  prepotent  over  the  pollen-borne  characters  of  the 
new  form,  supposing  that  fertilization  actually  took  place.  It 
is  obvious  that  more  extensive  experiments  should  be  made  in 
an  effort  to  secure  reciprocal  crosses  between  the  species  and  the 
variety. 

Webber  has  expressed  the  following  opinion :  "  Of  the  various 
causes  of  origin  it  seems  to  me  most  reasonable  to  assume  that  it 
is  a  mutant  and  the  type  of  mutation  to  nanate  form  is  similar 
to  Oenothera  nanella  and  the  Cupid  Sweet  Pea.  One  finds  par- 
allel cases  of  partial  reversion  to  the  parent  type  among  De 
Vriesian  mutations." 

The  reasons  for  thinking  the  new  form  may  have  originated 
through  mutations  in  otherwise  normal  flowers  of  J.  calif  ornica 
may  be  stated  briefly  as  follows : 

1.  In  the  1911  recurrence  of  the  new  form  in  Garden  Grove, 
it  was  found  by  actual  examination  of  the  seed  bed  that  all  of 
the  aberrant  seedlings  examined  grew  from  nuts  of  normal  size 
and  shape. 

2.  The  crop  of  1912  from  a  certain  tree  of  Juglans  calif  or- 
nica (No.  16  in  the  Garden  Grove  row  above  mentioned)  has 
produced  several  seedlings  of  the  new  form.  The  nuts  from 
which  they  grew  are  of  normal  size  and  shape.  The  possibility 
of  hybridization  with  any  species  of  oak  or  other  species  of 
walnut  is  very  remote. 

3.  The  large  tree  standing  close  to  No.  16  is  known  to  have 
been  the  source  of  many  of  the  nuts  planted  in  Tyler's  nursery 
in  the  years  when  quercina  seedlings  appeared  in  his  seedbeds. 
On  this  account  it  was  suspected  of  being  the  source  of  the  new 
form.  It  appears,  however,  that  No.  16  has  been  the  source  of 
some  quercina  seedlings  and  that  the  particular  seeds  that  save 
rise  to  it  were  produced  on  the  branches  nearest  the  tree  origin- 
ally suspected. 

Transmitted  May  9,  1913. 


PLATE  1 

Juglans  californica  var.  querdna  Babeock 

Fig  1. — Disher's  original  trees  in  Garden  Grove,  Cal.  The  one  ;it 
the  left  bears  regularly,  the  other  produces  only  staminate  or  very  rarely 
abortive  pistillate  flowers. 


[24] 


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I 'LATH   2 

Juglans  California!  var.  quercina  Rabcock 
Fig.  2. — Leaves  and  nuts  from  Disher's  original  fertile  tree.     X  1. 

Fig.  '■'>. —  Normal  leaf  (a)    fr the  Leffmgwell  original   tire  and   four 

leaves  from  the  same  tree  bearing  ascidia.      ■    ' .... 


[26] 


UNIV.   CALIF.    PUBL,   AGR.    SCI.    VOL.   2 


[BABCOCK]    PLATE  2 


3 


PLATE  3 

Juglans  calif ornica  var.  qui  rcina  Babcock 

Fig.  4. — Twigs  with  partially  developed  fruits  from    Disher's  original 
fertile  tree.     X  %. 

.Indians  calif  ornica  var.  quercina  Babcock 

Fig.   5. — Twigs   with   fruits   from   Disher's  original    fertile    tree    and 
a  twig  bearing  late  flowers  from  the  same  tree.     X  %. 


[28] 


UNIV.   CALIF.    PUBL.   AGR.    SCI.    VOL.   2 


[BABCOCK]    PLATE  3 


4 


5 


PLATE    I 

Juglans  ealifornica    Wats. 
Pig.   6.   -a.   b,   r.   d,   '.   nuts   sectioned    transversely;    f,   exterior   of   one 

Milt.         X     1. 

Juglans  ealifornica  var.  quercina   Bal ek 

Pig.  6.—  g,  It.  i,  /.  I.,  nuts  sectioned  tranversely;  ',  exterior  of  one  nut. 
X  1. 


[30] 


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PLATE  5 

Juglans  calif omica  var.  quercina  Babcock 

Fig.   7. — First  recurrence  of  the   new  form.     A   two-year-old   seedling 
at   Garden   Grove    in    1907. 

Fig.    8. — Leaf    from    another    seedling    of    the    same    lot    as    the    one 
shown  in  fig.  7.     X  1. 


[32] 


UNIV.    CALIF.    PUBL.   AGR.   SCI.    VOL.   2 


[BABCOCK]  PLATE  5 


Lr<l  m 1  1 

1 ;  B               "*?*-'• 

7r<<  * 

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p'-kj^JflPGh 

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7 


PLATE  6 

Juglans  californica  var.  quercina  Babcock 

Fig.   9. — Flowers  from   Disher  's   original    tree   in   1913;    (a)    male,    (b) 
female.     X  1. 

Juglans  californica  Wats. 
Fig.  10. — Normal  flowers;   (a)   male,  (b)   female.     X  1. 


[34] 


UNIV.    CALIF.    PUBL.   AGR.    SCI.    VOL.    2 


[BABCOCK]    PLATE  6 


a 


9 


a 


PLATE  7 

Juglans  californica  Wats. 
I^ig.  11. — Normal  leaves  and  fruits.  >•_.. 


[36] 


UNIV.    CALIF.    PUBL.   AGR.    SCI.   VOL.   2 


[BABCOCK]    PLATE  7 


PLATE  8 

Juglans  calif ornica   Wats. 

Fig.  12. — a.  Ts'ormal  pistillate  catkin  with  a  developing  nut;  b.  Abnor- 
mal catkin  with  pistillate  flowers;  c.  Shows  asymmetry  of  the  abnormal 
flowers;  d.  Shows  depression  in  surface  of  ovary;  i.  A  bisexual  flower. 
X  1. 


[38] 


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PLATE  9 

Juglans  californica  Wats. 

Fig.  13. — Abnormal  fruits — a,  b,  c,  type  x;  d,  e,  type  y. 

a',  V,  c' ,  d',  e'.     Abnormal  nuts  from  similar  fruits. 

a",  b" ,  c" ,  d",  c".  Similar  nuts  sectioned  transversely  and  placed  in 
relatively  the  same  position,  the  basal  portions  being  uppermost  in  the 
figure.     All  X  %. 

Fig.  14. — Abnormal  leaves — a,  b,  c,  from  second-growth  lateral 
branchlets;  d,  e,  f,  associated  with  abnormal  catkins;  all  collected  from 
wild  trees  in  Brea  Canon  in  1909.     X  %. 


[40J 


UNIV.   CALIF.    PUBL.   AGR.    SCI.    VOL.   2 


[BABCOCKJ    PLATE  9 


a 


d 


a 


IB 


a 


b 


jj> 


*»■ 


b" 


13 


d 


d 


%■ 


PLATE  10 

Fig.  15. — a,  Abnormal  leaf  on  a  second-growth  lateral  branchlet  on 
Juglans  calif  ornica,  Brea  Canon,  1909;  b,  a  typical  leaf  from  the  Leffing- 
well  quercina  tree.     X  %. 

Fig.  16. — One  of  the  three  original  quercina  trees  at  N.  B.  Pierce's 
gardens  in   Santa   Ana,   1913. 


[42] 


UNIV.   CALIF,    PUBL,   AGR.   SCI.    VOL.   2 


[BABCOCK]    PLATE    10 


a 


15 


PLATE  11 

Juglans  calif ornica  var.  quercina  Babcock 

Fig.  17.- — Abnormal  late  catkins  from  the  Leffingwell  tree;  o,  normal 
catkin  bearing  one  young  fruit  and  with  an  abnormal  catkin  growing 
from  its  base;  b,  c,  d,  abnormal  catkins  and  leaves.     X  %. 

Fig.  18. — Two  seedlings  from  Juglans  calif  ornica  tree  No.  16  (Garden 
Grove),  March,  1913;  a,  typical  of  the  species;  b,  quercina  form.     X  %. 


[44] 


UNIV.   CALIF.    PUBL.   AGR,    SCI.    VOL.    2 


[BABCOCK]    PLATE   II 


PLATE   12 

Juglans  califormea   Wats. 
Pig.   19.— Tree  No.   Hi.  Garden  Grove,  April,    L913. 


I  46  | 


UNI7.   CALIF.    PUBL.   AGR.    SCI.    VOL.    2 


[BABCOCK]    PLATE   12 


UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  2,  No.  2,  pp.  47-70,  pis.  13-19  October  31,  1914 


STUDIES  IN  JUGLANS  II 

FURTHER   OBSERVATIONS   ON  A   NEW  VARIETY   OF 

JUGLANS    CALIFORNICA    WATSON    AND    ON 

CERTAIN  SUPPOSED  WALNUT-OAK 

HYBRIDS 

BY 

ERNEST  B.  BABCOCK 


In  the  preceding  paper  on  this  subject1  appeared  the  history 
and  description  of  a  new  form  of  California  Black  Walnut,  which 
was  named  Juglans  californica  var.  quercina,  together  with  a 
discussion  of  several  hypotheses  regarding  its  nature  and  origin. 
The  following  hypotheses  were  deemed  worthy  of  serious  consid- 
eration and  feasible  as  bases  for  further  study : 

(1)  Origin  through  hybridization  with  the  Coast  Live  Oak, 
Quercus  agri  folia  Nee. 

(2)  Origin  from  teratological  flowers  and  fruits  of  J.  cali- 
fornica. 

(3)  Origin  by  mutations  in  apparently  normal  flowers  and 
fruits  of  J.  californica. 

In  order  to  test  the  first  hypothesis,  that  of  origin  through 
hybridization  between  walnut  and  oak,  attempts  to  hybridize  the 
two  species  were  made  in  the  years  1908  to  1911,  inclusive.  As 
a  result  of  the  pollination  work  in  1908,  fifty-six  seedlings  were 
secured  from  nuts  that  developed  from  pistillate  walnut  flowers 
which  had  been  pollinated  with  oak  pollen  under  bag.  Except 
for  considerable  variation  in  size,  these  trees  have  not  exhibited 
more  differences  than  would  be  found  among  ordinary  trees  of 


48  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

J.  californica  growing  in  the  wild.  However,  since  in  certain 
known  interspecific  hybrids  the  Ft  plants  all  resemble  the  female 
parent,  it  was  deemed  advisable  to  grow  at  least  the  second 
generation  from  all  these  trees.  In  1913  thirty  of  them  bore 
imts,  which  were  collected  and  stratified.  Also  in  the  spring  of 
1913  large  paper  bags  were  placed  on  most  of  these  trees  enclos- 
ing flowers  of  both  sexes  in  order  to  insure  self-pollination  of  a 
few  flowers  on  each  tree.  These  bags  were  shaken  vigorously 
several  times  during  anthesis  and  upon  examination  of  several 
flower  clusters  the  stigmas  were  found  to  be  well  covered  with 
pollen.  Very  few  nuts  developed  under  bag,  but  this  may  not 
have  been  due  to  self -sterility  on  the  part  of  the  individual  trees. 
A  period  of  very  warm  and  humid  weather  caused  most  of  our 
walnut  flowers  that  were  developing  under  bag,  both  in  Southern 
California  and  at  Berkeley,  to  drop.  From  the  self-pollinated 
nuts  secured  on  these  supposed  hybrids  75  seedlings  from  24 
different  trees  are  growing.  These,  together  with  2001  seedlings 
from  naturally  pollinated  nuts  representing  30  different  trees. 
give  a  total  of  2076  second  generation  seedlings  that  have  been 
examined.  Among  them  all  not  a  single  individual  has  been 
found  that  resembles  the  new  variety.  Neither  is  there  any  indi- 
cation of  oak  characters  in  these  F.2  seedlings.  Therefore  as  yet 
we  have  no  evidence  that  the  Ft  trees  are  true  hybrids.  A  suffi- 
cient number  of  F2  plants  will  be  retained  to  grow  the  F:!  gener- 
ation from  each  Ft  tree. 

Now  the  question  arises  as  to  the  nature  of  the  supposed  F, 
hybrids.  I  consider  the  conditions  under  which  the  work  of 
pollination  was  performed  in  1908  to  have  been  practically  ideal. 
The  pistillate  flowers  were  bagged  long  before  any  walnut  trees 
were  shedding  pollen.  On  one  of  the  two  trees  I  am  certain 
that  no  pollen  was  being  shed  even  at  the  time  I  pollinated. 
This  tree  was  fairly  well  isolated  from  other  walnuts,  some  of 
which  were  shedding  pollen  at  that  time.  Moreover,  no  nuts 
developed  in  the  check  bags  on  this  tree.  Now  if  natural  polli- 
nation was  prevented  both  before  and  after  the  application  of 
oak  pollen,  why  are  not  these  trees  hybrids  ?  Are  they  the  result 
of  abnormal  embryogeny  due  perhaps  to  stimulation  by  the  oak 
pollen  but  without  the  occurrence  of  fertilization  ?     It  should 


1914]  Babeock:  New  Variety  of  Juglans  49 

be  remembered  that  they  are  the  progeny  of  only  two  different 
trees  and.  if  they  are  the  result  of  asexual  reproduction,  it  would 
be  reasonable  to  expect  among  the  offspring  of  either  parent 
marked  uniformity  in  size,  leaf  characters,  time  of  putting  forth 
and  shedding  leaves,  time  of  flowering  and  flower  characters. 
But  the  variations  in  the  above  mentioned  characteristics  are 
so  great  as  to  suggest  heterogeneous  parentage  within  the  species 
rather  than  asexual  reproduction  from  one  or  two  parent  trees. 
Plate  13.  figure  1,  and  plate  14,  figure  2,  show  a  typical  leaf  and 
a  cluster  of  partly  developed  fruits  from  each  of  six  of  these 
Fl  seedlings. 

With  these  facts  in  mind,  let  us  consider  briefly  the  various 
processes  of  abnormal  embryogeny  that  may  have  given  rise  to 
these  variable  seedlings.  (1)  The  new  sporophyte  may  have 
developed  from  the  megaspore  mother-cell,  in  which  case  its 
cells  would  possess  the  diploid  number  of  chromosomes  charac- 
teristic of  Juglans  calif ornica,  provided  that  the  parent  tree  was 
typical  of  the  species.  (2)  It  may  have  arisen  from  the  mega- 
spore,  from  the  egg  nucleus,  or  from  one  of  the  other  embryo 
sac  nuclei,  without  fertilization,  in  which  case  its  cells  would 
contain  the  haploid  number  of  chromosomes.  (3)  It  may  have 
arisen  adventitiously  from  sporophytic  tissue,  in  which  case  its 
cells  would  contain  the  diploid  number  of  chromosomes.  It  is 
obvious  that  in  either  the  first  or  third  instances  we  should  ex- 
pect much  uniformity  among  the  progeny  and  close  resemblance 
to  the  parent  trees.  Hence,  in  view  of  the  wide  variation  men- 
tioned above,  it  is  reasonable  to  assume  the  occurrence  of  one 
or  more  of  the  three  phases  of  parthenogenesis  included  in  the 
second  of  the  three  cases  above  defined. 

Finally,  this  hypothesis  of  origin  by  hybridization  with  oak 
is  practically  annihilated  by  the  discovery  previously  reported 
that  in  a  row  of  twenty-one  California  Black  Walnuts,  growing 
in  Garden  Grove,  Orange  County,  California,  a  single  tree  has 
been  found  which  produces  the  new  variety  year  after  year.  I 
know  of  no  oaks  in  this  region,  but  even  if  oaks  were  abundant 
and  close  at  hand,  the  fact  that  quercina  seedlings  come  from 
only  one  tree  would  certainly  indicate  some  other  cause  than 
oak  pollination. 


50  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

As  for  the  second  hypothesis,  that  the  new  variety  originated 
from  teratological  flowers  of  J.  calif  omica,  this  seemed  very 
unlikely  after  testing  sixty-eight  abnormal  nuts  from  several 
different  trees  and  failing  to  secure  it,  and  especially  after  dis- 
covering that  the  new  form  does  originate  from  nuts  of  normal 
appearance.  At  the  same  time,  the  occurrence  of  teratological 
leaves,  flowers,  and  fruits  in  this  species  would  certainly  indicate 
an  unstable  condition,  which  finds  its  most  frecpient  expression 
in  these  abnormal  features  of  the  somatoplasm  and  which  may 
occasionally  result  in  such  segregations  in  certain  cell  divisions 
preceding  or  accompanying  gametogenesis  as  would  result  in 
what  we  call  mutation.  As  a  matter  of  fact  the  tree  of  J.  cali- 
fomica,  mentioned  above,  which  has  been  under  observation  about 
two  years  (tree  no.  16  mentioned  at  the  close  of  the  preceding 
paper),  produced  in  1913  a  few  clusters  of  these  abnormal  late 
nuts.  These  were  found  while  gathering  the  normal  nuts  from 
this  tree.  Each  cluster  (produced  on  a  single  catkin)  was  gath- 
ered separately  and  given  a  number.  A  tree  label  bearing  the 
same  number  was  attached  to  the  twig  that  bore  that  particular 
cluster.  From  each  of  three  of  these  clusters  of  teratological 
fruits  two  or  more  quercina  seedlings  have  appeared.  Plate  15, 
figure  3,  shows  the  seedlings  grown  from  abnormal  cluster  number 
B4  which  was  borne  on  a  late-appearing  catkin  which  sprang 
from  the  base  of  a  normal  pistillate  catkin  on  twig  number  151. 
In  this  case  there  are  four  typical  calif omica  plants  {a,  b,  c,  d), 
four  quercina  plants  (e,  f,  g,  h),  and  two  seeds  that  did  not 
germinate.  It  may  be  questioned  whether  seedling  h  could  be 
properly  classified  at  such  an  early  stage.  Suffice  it  to  say  that, 
even  at  the  time  when  the  stem  is  just  pushing  through  the  soil, 
the  appearance  of  quercina  is  quite  distinct  from  that  of  cali- 
f omica.  Seen  from  above  the  former  has  the  shape  of  a  rosette 
while  the  latter  appears  as  a  cone.  This  is  due  to  the  decided 
difference  in  the  apices  of  the  leaves  (cf.  b  and  e).  Seedling  h 
presents  a  fine  exhibition  of  geotropism  due  to  the  position  in 
which  the  seed  happened  to  be  planted.  The  extreme  abnormality 
of  some  of  the  nuts  of  this  cluster  is  strikingly  shown  in  a,  c,  e 
and  /.  In  each  of  these  seeds  one  cotyledon  was  confined  within 
a  sector  equal  to  about  one-third  the  volume  of  the  nut.     It  is 


1914]  Babcock:  New  Variety  of  Juglans  51 

obvious  that  there  is  no  relation  between  degree  of  abnormality 
of  the  nut  and  the  appearance  of  the  quercina  form.  However, 
the  fact  that  quercina  seedlings  have  been  secured  from  terato- 
logical  fruits  might  seem  to  indicate  that  in  this  fact  of  tera- 
tology one  finds  the  basis  for  a  complete  solution  of  the  problem 
in  hand.  But  these  are  the  first  quercina  seedlings  I  have  raised 
from  abnormal  nuts,  and  of  the  twenty-eight  seedlings  secured 
only  eleven  are  quercina  in  character.  On  the  other  hand,  all 
the  young  quercina  seedlings  examined  in  the  past  have  sprung 
from  apparently  normal  nuts.  This  shows  that  something  more 
than  the  mere  fact  of  teratology  must  be  found  to  explain  the 
origin  of  the  new  variety. 

Regarding  the  third  hypothesis  the  evidence  now  at  hand  is 
definite  and  sufficient.  Over  three  hundred  clusters  of  normal 
nuts  were  gathered  separately  from  tree  No.  16  in  1913,  fol- 
lowing the  method  described  above.  The  number  of  nuts  per 
cluster  varied  from  one  to  five.  The  nuts  of  each  cluster  were 
stratified  in  a  pot  bearing  the  same  label  as  the  twig  from  which 
the  cluster  came.  Later  the  pots  were  transferred  to  a  cool  green- 
house where  they  were  kept  until  the  plants  were  several  inches 
high.  One  quercina  seedling  was  found  in  each  of  42  pots.  Plate 
16,  figure  4,  shows  the  seedlings  from  the  two  nuts  in  cluster  35 ; 
plate  17,  figure  5,  shows  the  seedlings  from  cluster  97 ;  and  plate 
18.  figure  6,  the  seedlings  from  cluster  196.  Besides  the  600 
seedlings  grown  from  marked  clusters  of  nuts,  about  1000  addi- 
tional seedlings  were  raised  from  this  tree.  Of  the  total  num- 
ber of  seedlings  grown  approximately  5  per  cent  were  quercina. 

The  fact  that  among  the  normal  fruits  of  this  particular  tree 
only  one  nut  in  a  cluster  produces  the  quercina  form,  at  once 
suggests  a  possible  relation  between  location  in  the  cluster  and 
production  of  quercina  seedlings.  Observations  and  experiments 
are  being  conducted  in  order  to  determine  whether  there  is  any 
definite  position  in  the  cluster  or  other  morphological  feature 
that  is  associated  with  origin  of  the  new  form. 

The  nuts  gathered  from  this  tree  in  1913  may  not  have  been 
self-pollinated.  About  four  hundred  branchlets  including 
staminate  and  pistillate  flowers  were  bagged  in  early  spring,  but 
the  warm  moist  weather  mentioned  above  caused  all  the  pistillate 


52  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

flowers  to  drop.  Thus  my  only  recourse  was  to  label  and  bag 
clusters  of  developing  nuts.  About  350  clusters  were  so  treated. 
It  is  very  likely  that  many  of  the  flowers  were  cross-fertilized 
with  pollen  from  neighboring  trees.  However,  if  the  pollen  of 
either  no.  16  or  its  near-by  neighbors  had  been  the  source  of  the 
new  form,  quercina  seedlings  should  have  been  obtained  among 
the  progeny  of  other  trees  besides  no.  16  in  the  original  seed  test 
made  in  1912.  Since  only  the  one  tree  produces  the  new  form 
I  have  disregarded  pollination  for  the  present,  studying  only  the 
pistillate  flowers  and  testing  the  seeds. 

Cytological  investigation  will  possibly  reveal  the  true  nature 
of  the  new  form  and  perhaps  explain  its  origin.  Meanwhile  the 
speculations  concerning  the  nature  of  the  supposed  walnut-oak 
hybrids  are  suggestive  in  this  connection.  Through  failure  of 
pollination  or  fertilization  parthenogenesis  may  take  place.  That 
polyembryony  occurs  both  in  the  new  form  and  the  old  is  proved 
by  the  discovery  of  the  specimens  shown  in  plate  19,  figures  7 
and  8.  In  each  case  the  two  embryos  were  complete,  each  caulicle 
being  attached  to  its  own  pair  of  cotyledons.  Again,  it  is  possible 
that  at  some  stage  in  flower  development  abnormal  mitosis  oc- 
curs. Should  this  happen  in  a  very  early  stage  in  the  develop- 
ment of  the  flower,  sufficient  abnormal  somatic  tissue  would  be 
produced  to  make  cytological  investigation  comparatively  easy. 
It  is  hoped  that  by  determining  the  morphological  location  of  the 
nuts  that  produce  quercina  seedliims  the  cytological  study  of 
very  young  flower  clustei's  will  lie  somewhat  simplified. 

The  present  tendency2  to  refer  to  hybridization  as  the  basis 
of  all  variation  calls  for  a  reference  to  my  previous  paper1  where 
I  discussed  the  hypothesis  of  origin  through  hybridization  either 
with  oak  or  with  any  form  of  Jiii/laiix  and  allied  genera,  and 
showed  that  such  a  hypothesis  is  untenable.  The  results  reported 
in  this  paper  bear  out  that  conclusion.  Further,  as  opposed  to 
the  proposition  of  assuming  hybridization  as  necessary  for  the 
occurrence  of  mutation,  we  have  the  reeenl  conclusion  of  Gates3 
"that  mutation  and  hybridization  are  separate  phenomena,  and 
that  the  cause  of  some  at  least  of  the  mutations  in  (Enolhera  is 
independent  of  the  combination  of  hybrid  characters." 


1914]  Babcoclc:  New  Variety  of  J 'uglans  53 

The  origin  of  quercina  is  similar  to  those  transmutations  in 
Lycopersicum,4  Gossypium,5  Nicotiana,0  and  Oenothera,3  which 
have  been  described  as  aggregate  mutations  as  distinguished 
from  loss  or  addition  of  single  characters  as,  for  example,  in 
Helianthus7  and  Drosophila*  In  regard  to  the  tobacco  mutation 
above  referred  to,  the  authors6  assume  ' '  that  mutation  must  have 
taken  place  after  fertilization,  i.  e.,  after  the  union  of  the  male 
and  female  reproductive  cells."  Castle9  suggests  it  is  equally 
probable  that  the  mutation  occurred  in  an  egg  cell  which  then 
developed  without  fertilization  since  "parthenogenesis  is  known 
to  occur  in  tobacco  and  mutation  in  a  growing  or  immature  germ 
cell  seems  inherently  more  probable  than  in  a  fully  formed  and 
fertilized  one."  This  discussion  is  pertinent  to  both  phases  of 
the  problem  herein  set  forth,  viz.,  first,  an  explanation  of  the 
variation  found  in  the  Fx  oak-pollinated  walnut  seedlings ;  second, 
the  cytological  time  of  the  mutations  that  produce  quercina 
seedlings. 

Concerning  the  first  question,  parthenogenesis  or,  more  specif- 
ically, apogamy,  assuming  the  occurrence  of  reduction  in  chromo- 
some number,  might  explain  the  variation  in  the  Fx  oak-pollinated 
seedlings  whereas  such  an  extent  of  variation  is  too  great  to 
permit  the  assumption  that  embryos  developed  from  the  spore 
mother  cell  or  other  sporophytic  tissue  without  also  assuming 
irregularities  in  chromosome  behavior.  Reduction  is  not  assumed10 
in  the  classical  cases  of  parthenogenesis  in  angiosperms  (Anten- 
naria,  Taraxacum,  Hieracium  and  Alchemilla) ,  but  in  Thalicirum 
purpurascens  Overton11  finds  "the  development  and  germination 
of  the  megaspore  is  that  usually  found  among  angiosperms."  He 
reports  no  observations  on  chromosome  behavior  but  shows  that 
"parthenogenesis  is  becoming  fixed  in  Thalictrum."  In  such  an 
instance  it  seems  reasonable  to  assume  that  the  omission  of  reduc- 
tion has  become  established  also.  But  in  Juglans  the  existence 
of  adaptation  for  wind  pollination  would  indicate  that  pollination 
and  fertilization  are  usually  essential  for  seed  production  and 
there  is  experimental  proof1  of  this  also.  Moreover,  the  extensive 
researches  of  Nawaschin  and  Finn12  on  the  cytology  of  fertiliza- 
tion in  Juglans,  although  lacking  the  treatment  of  chromosome 
number  and  behavior,  demonstrate  that  the  process  of  fertiliza- 


54  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 

tion  is  typically  chalazogamous,  there  being  a  well-developed  bi- 
nucleate  cell  which  reaches  the  embryo  sac.  Hence  the  occurrence 
of  reduction  may  be  assumed,  in  which  case  embryos  must  arise 
through  apogamy  in  the  absence  of  fertilization.  But  with  the 
haploid  number  of  chromosomes  in  the  somatic  tissue  of  these 
seedlings,  as  will  be  shown  below,  one  might  expect  even  greater 
deviations  from  the  parent  forms  than  actually  occur.  Thus, 
if  apogamy  and  reduction  be  assumed,  it  seems  necessary  also 
to  assume13  "the  subsequent  arrest  of  the  homotypic  mitosis 
(in  the  cell  destined  to  differentiate  the  embryo  sac)  before  the 
division  of  the  nucleus  has  taken  place,  resulting  in  the  pro- 
duction of  a  functional  germ  cell  with  a  chromosome  number 
double  that  of  its  reduced  number. ' ' 

Regarding  the  other  question,  the  mutations  that  produce 
quercina  seedlings  evidently  occur  only  in  pistillate  calif  ornica 
flowers,  thus  producing  seedlings  that  will  not  breed  true.  This 
indicates  that  the  cytological  time  of  mutation  is  previous  to 
fertilization. 

From  her  cytological  studies  of  Oenothera  Lutz14  has  con- 
cluded that  "all  individuals  of  a  given  type  of  vegetative  char- 
acter invariably  have  identical  somatic  chromosome  numbers 
regardless  of  the  diversity  of  origin  of  the  individuals  in  ques- 
tion," and,  further,  that  "All  individuals  .  .  .  having  a  chro- 
mosome number  much  in  excess  of  that  in  O.  Lamarckiana  dis- 
played certain  characters  strongly  suggesting  those  of  0.  gigas, 
chiefly  noted  in  the  stoutness  of  all  parts."  This  suggests  that 
in  a  form  like  quercina,  which  is  reduced  in  all  vegetative  char- 
acters, we  should  expect  to  find  the  somatic  number  of  chromo- 
somes to  be  less  than  the  number  typical  of  the  species. 

The  occurrence  of  such  a  mutation  in  Juglans  is  of  especial 
significance  because  of  the  phylogenetic  relationships  ascribed 
to  these  chalazogamous  forms.  According  to  Nawaschin  and 
Finn,12  the  preservation  of  the  male  cytoplasm  in  the  species  of 
Juglans  indicates  an  old  tendency  inherited  from  gymnosperm 
ancestors  and  furnishes  further  important  proof  of  the  great  age 
of  these  forms,  which  stand  on  the  threshold  of  the  angiosperm 
world.  Berry15  mentions  the  occurrence  of  seven  species  of 
Juglans   in   the   upper   Cretaceous   deposits,   twenty-five   in   the 


1914]  Babcock:  New  Variety  of  Juglans  55 

Eocene,  several  in  the  Oligocene,  upwards  of  twenty  in  the 
Miocene,  and  about  twenty-five  in  the  Pliocene,  several  of  the 
latter  being  very  close  to,  if  not  identical  with,  existing  species. 
These  are  what  remain  in  the  very  imperfect  geological  record. 
Doubtless  many  others  existed.  Now  that  aggregate  mutation 
is  known  to  have  occurred  once  in  such  a  group,  it  is  reasonable 
to  assume  the  occurrence  of  such  major  discontinuous  variations 
as  one  of  the  processes  by  which  new  species  have  been  produced. 
A  recent  effort1"  to  harmonize  the  older  theories  of  evolution 
through  continuous  variation  and  the  modern  conception  of 
alternative  inheritance  assumes  that  "unit  characters"  are  really 
composite  in  nature,  but  the  paleobotanist  will  not  necessarily 
accept  the  hypothesis  that  all  new  species  were  built  up  from 
such  minute  discontinuous  variations  that  the  effect  is  one  of 
continuous  though  gradual  change.  It  is  just  as  reasonable  to 
assume  that  the  fossil  species  sprang  into  existence  in  the  same 
sudden  manner  as  that  by  which  quercina  made  its  appearance. 
On  account  of  the  persistent  assumption  by  some17  that 
quercina  is  a  natural  hybrid  between  walnut  and  oak  and  that 
the  progeny  of  the  original  quercina  trees  are  composed  of  walnut 
and  oak  seedlings  in  Mendelian  proportions,  it  should  be  noted 
that  there  is  wide  variation  among  the  fruiting  specimens  of  the 
new  form  as  to  the  proportion  of  californica  and  quercina  seed- 
lings they  produce.  I  have  tested  seeds  from  three  of  the  original 
trees  distributed  by  Disher1  and  find  they  differ  very  widely  in 
this  respect.  They  certainly  produce  no  oaks  and  there  is  no 
basis  for  assuming  a  Mendelian  ratio  among  the  progeny. 


56  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  2 


SUMMARY 

1.  The  belief,  which  has  been  held  by  many,  that  the  new 
form  of  walnut,  Juglans  californica  var.  quercina,  originated 
through  hybridization  between  walnut  and  oak  is  without  founda- 
tion in  fact.  There  is  no  evidence  that  hybridization  with  other 
species  of  walnut  or  cross-pollination  with  other  trees  of  the  same 
species  causes  the  appearance  of  the  new  form. 

2.  Although  abnormal,  late  appearing  flowers  and  fruits  oc- 
cur rather  frequently  on  the  California  Black  Walnut,  only  one 
tree  has  been  found  to  produce  abnormal  nuts  which  give  rise  to 
quercina  seedlings,  and  more  than  half  of  the  abnormal  nuts  from 
this  particular  tree  produce  typical  californica  plants.  Certainly 
teratology  cannot  be  considered  the  cause  of  the  origin  of  the  new 
variety. 

3.  The  evidence  that  seedlings  of  the  new  variety  come  from 
certain  apparently  normal  nuts  is  conclusive,  since  a  tree  has 
been  located  that  annually  produces  a  small  percentage  of  quer- 
cina seedlings.  Evidently  these  aberrant  individuals  are  the  re- 
sult of  internal  changes  that  take  place  during  the  growth  of  the 
flowers  previous  to  fertilization.  It  is  possible  that  evidence  of 
these  changes  will  be  discovered  by  microscopical  study  of 
material  from  tree  no.  16  and  that  further  breeding  experiments 
will  help  to  explain  them.  Meanwhile,  whether  the  true  nature 
of  these  changes  be  revealed  or  not,  we  know  that  embryos  are 
produced  independently  of  the  influence  of  self-  or  cross- 
pollination,  which  are  capable  of  developing  into  individuals  pos- 
sessing characters  strikingly  different  from  those  of  the  parent 
and  capable  of  transmitting  those  same  characters  to  at  least  a 
portion  of  their  progeny.  Such  occurrences  of  discontinuous 
variation  are  generally  recognized  as  mutations,  and  the  quercina 
walnut  is  similar  to  certain  mutations  in  tomato,  cotton,  tobacco 
and  evening  primrose,  which  have  been  designated  as  aggregate 
mutation. 

Transmitted  June  15,  1914. 


1914]  Babcock:  New  Variety  of  Juglans  57 


PUBLICATIONS  REFERKED  TO  IN  THIS  PAPER 

1  Babcock,  E.  B.,  Study  of  a  New  Form  of  Juglans  calif  omica  Watson, 
Univ.  Calif.  Pub).  Agric.  Sciences,  vol.  2,  no.  1,  1913. 

2  Bateson,  Wm.,  Address  of  the  President  of  the  British  Association 
for  the  Advancement  of  Science  at  Melbourne,  Science,  n.  s.,  vol.  40,  no. 
1026,  p.  296,  1914. 

s  Gates,  R.  R.,  Breeding  experiments  which  show  that  hybridization 
and  mutation  are  independent  phenomena,  Zeitschr.  f.  Ind.  Abstamm.-u 
Vererbungslehre,  bd.  11,  hft.  4,  1914. 

4  White,  Chas.  A.,  The  Mutations  of  Lycopersicum,  Pop.  Sci.  Mo.,  vol. 
67,  no.  2,  p.  151,  1905. 

s  White,  Chas.  A.,  Aggregate  Mutations  in  Gossypium,  Science,  n.  s., 
vol.  27,  no.  683,  1913;  and  Cook,  O.  F.,  Mutative  Reversions  in  Cotton, 
Circ.  no.  53,  Bur.  Plant  Industry,  U.  S.  Dept.  Agric,  1910. 

6  Hayes,  H.  K.,  and  Beinhart,  E.  G.,  Mutation  in  Tobacco,  Science,  n.  s., 
vol.  39,  no.  992,  p.  34,  1914. 

7  Cockerell,  T.  D.  A.,  The  Red  Sunflower,  Pop.  Sci.  Mo.,  vol.  80,  no.  4, 
p.  373,  1912;  A  Wine-Eed  Sunflower,  Science,  n.  s.,  vol.  38,  no.  974,  p.  312, 
1913;  Suppression  and  Loss  of  Characters  in  Sunflowers,  ibid.,  n.  s.,  vol. 
40,  no.  1025,  p.  283,  1914. 

s  Morgan,  T.  H.,  Heredity  and  Sex,  1913. 

0  Castle,  W.  E.,  The  Cytological  Time  of  Mutation  in  Tobacco,  Science, 
n.  s.,  vol.  39,  no.  995,  p.  140,  1914. 

i°  Strasburger,  Noll,  Schenck  and  Karston,  A  Text-Book  of  Botany, 
p.  93,  1908. 

n  Overton,  Jas.  B.,  Parthenogenesis  in  Thalictrum  purpurascens,  Bot. 
Gaz.,  vol.  33,  p.  363,  1902. 

i2  Nawaschin,  S.,  and  Finn,  V.,  Zur  Entwickelungsgeschichte  der  Chala- 
zogamen,  Juglans  regia  and  J.  nigra,  in  Mem.  Acad.  Imp.  Sci.  St.  Peters- 
bourg,  31,  pp.  1-59,  1913.  Also  noted  in  Bot.  Gaz.,  vol.  57,  no.  2,  p.  162, 
1914. 

is  This  is  the  5th  condition  of  Gregoire's  hypothesis  for  explaining 
chromosome  numbers  in  (Enothera  as  set  forth  by  Lutz  (cf.  14,  p.  426). 

i*  Lutz,  Anne  M.,  Triploid  Mutants  in  Oenothera,  in  Biolog.  Central., 
bd.  32,  no.  7,  1912. 

15  Berry,  Edw.  W.,  Notes  on  the  Geological  History  of  the  Walnuts  and 
Hickories,  Plant  World,  vol.  15,  no.  10,  1912. 

10  Collins,  G.  N.,  Nature  of  Mendelian  Units,  Jour.  Heredity,  vol.  5, 
no.  10,  1914. 

17  Pierce,  N.  B.,  A  New  Walnut,  Science,  n.  s.,  vol.  37,  no.  955,  p.  613, 
1913. 


PLATE  13 

Juglans  californica   X   Quercus  agrifolia 

Fig.  1. — a,  leaf  and  fruits  from  F  seedling  No.  13a. 
Fig.  1. — b,  leaf  and  fruits  from  F  seedling  No.  13b. 
Fig.  1. — e,  leaf  and  fruits  from  F    seedling  No.  13c. 

The  nuts  from  which  these  three  F  seedlings  grew  were  borne  in  the 
same  cluster  on  J.  californica  tree  I  of  1908  hybridization  experiments. 
X    %. 


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PLATE  14 

Juglans  californica   X   Quercus  agrifolia 

Fig.  2 — a,  leaf  and  fruits  from  F!  seedling  No.  23a. 

Fig.  2 — b,  leaf  and  fruits  from  F,  seedling  No.  23b. 

Fig.  2 — c,  leaf  and  fruits  from  F,  seedling  No.  23c. 

The  nuts  from  which  these  three  F,  seedlings  grew  were  borne  in  the 
same  cluster  on  J.  californica  tree  II  of  1908  hybridization  experiments. 

X  y3. 


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PLATE  15 

Juglans  californica  Watson 

J.  californica  var.  quercina  Babcock 

Fig.  3. — a,  b,  c,  cl,  typical  californica  seedlings, — e,  f,  g,  h,  typical 
quercina  seedlings.  All  from  the  same  cluster  of  abnormal  fruits  from 
tree  No.  16  in  Garden  Grove,  Calif.     X   %. 


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PLATE  16 

Juglans  calif ornica  Watson 

J.  calif  ornica  v;ir.  qu<rcina  Babcock 

Fig.  4. — a,  quercina  and  b,  calif  ornica  seedlings  from  cluster  No.  35  on 
./.  calif  ornica  tree  No.  16  in  Garden  Grove,  Calif.     X   1. 


L64] 


UNIV.   CALIF.    PUBL.   AGR.   SCI.    VOL.   2 


[BABCOCK]    PLATE   16 


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PLATE  17 

Juglans  californica  Watson 

J.  californica  var.  qucrcina  Babcoek 

Fig.  •". — a,  qucrcina   and    b,   c, — californica   seedlings   from    cluster   No. 
97  on  J.  californica  tree  No.  16  in  Garden  Grove,  Calif.     X   %• 


[66] 


UNIV.   CALIF.    PUBL.   AGR.   SCI.    VOL.   2 


[BABCOCK]    PLATE   17 


PLATE  18 

Juglans  californica  Watson 

J.  calif  ornica  var.  quercina  Babcock 

Fig.  6. — a,    quercina    and    b,    c,    d, — californica    seedlings    from    cluster 
No.  196  on  J.  californica  tree  No.  16  in  Garden  Grove,  Calif.     X   V>. 


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PLATE  19 

Juglans  californica  Watson 

Fig.  7. — Specimen   of  polyembryony  from   cluster   No.   208  on  ,/.   cali- 
fornica tree  No.  16  in  Garden  Grove,  Calif.     X    '_•• 

Juglans   californica   var.   quercina   Babcock 

Fig.  8. — Specimen  of  polyembryony  from  a  cluster  of  abnormal  nuts 
on  J.  californica  tree  No.  16  in  Garden  Grove,  Calif.     X    '  •_>. 


[70] 


UNIV.   CALIF.    PUBL.   AGR.   SCI,    VOL.   2 


[BABCOCK]    PLATE   19 


UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  2,  No.  3,  pp.  71-80,  plates  20-21  September  20,  1916 


STUDIES   IN   JUGLANS,  III 

(1)   FURTHER    EVIDENCE    THAT    THE    OAK-LIKE 
WALNUT    ORIGINATES    BY    MUTATION 

BY 

EENEST  B.  BABCOCK 


In  previous  studies1  the  conclusion  was  reached  that  the  oak- 
like walnut,  Juglans  califomica  var.  quercina  Babcock,  was  first 
produced  as  a  result  of  germinal  variation  in  a  tree  of  the 
southern  California  black  walnut,  J.  califomica  Wats.,  and  that 
the  several  recurrences  of  this  peculiar  walnut  resulted  from 
repetitions  of  the  same  mutation.  It  is  the  purpose  of  this 
paper  to  report  further  evidence  showing  that  this  conclusion 
was  correct  at  least  as  regards  the  origin  of  the  first  quercina 
individual,  although  this  same  evidence  may  lead  to  a  different 
explanation  of  some  of  the  recurrences  of  this  form. 

This  evidence  consists  of  the  results  from  hybridizing  quercina 
and  califomica.  In  1908  pollen  from  the  original,  fertile,  type 
individual  of  quercina  was  applied  to  several  guarded  pistillate 
flowers  on  a  typical  califomica  tree.  The  eleven  Px  seedlings 
secured  are  growing  on  the  campus  of  the  University  of  Cali- 
fornia. They  are  all  normal  califomica  trees.  The  only  evidence 
of  heterosis  thus  far  observed  is  length  of  staminate  catkins, 
which  is  intermediate  between  the  two  parents.  In  1915  several 
of  these  Fx  trees  were  self-pollinated,  or  interpollinated,  and 
thirty-six  seeds  were  secured.  Up  to  the  present  eighteen  of  these 
have  germinated,  producing  twelve  califomica  and  six  quercina 


1  Babcock,  E.  B.,  Studies  in  Juglans  I  and  IT,  Univ.  Calif.  Publ.  Agric. 
Sciences,  vol.  2,  no.  1,  1913;   no.  2,  1914. 


72  University  of  California  Publications  in  Agricutlurdl  Sciences    [Vol.2 

seedlings,  which  is  a  ratio  of  2.67  to  1.33,  a  deviation  from  the 
theoretical  monohybrid  ratio  which  might  be  expected  to  occur 
under  the  laws  of  chance  in  42  per  cent  of  monohybrid  popu- 
lations. While  positive  statements  will  not  be  made  until  the 
F,  trees  have  been  tested  on  a  more  extensive  scale,  yet  a  valid 
:{  to  1  ratio  even  with  so  few  F2  individuals  is  certainly  an 
indication  that  the  genetic  relationship  between  califomiea  and 
guercina  is  a  difference  in  a  single  factor  of  the  same  Mendelian 
reaction  system. 

The  idea  that  a  single  factor-difference  may  so  affect  the 
entire  chromosome  system  that  the  individual  is  altered  more 
or  less  in  each  somatic  detail  is  now  generally  recognized,  yet 
the  direct  evidence  on  which  this  conception  is  based  is  found  in 
a  limited  number  of  cases.  Morgan2  refers  to  the  mutant  strains 
of  Drosophila  a>»p<  lopltila  called  "club"  and  "rudimentary", 
in  which  the  factor  for  a  certain  wing  character  also  conditions 
the  development  of  certain  other  morphological  and  physiological 
characters.  But,  thus  far  in  Drosophila,  no  single  factor  has 
been  found  thai  visibly  affects  every  external  feature  of  the 
organism.  The  well-known  dwarf  or  cupid  sweet  pea  is  a  strik- 
ing example  of  the  manifold  effects  of  a  single  factor.  This 
variety  differs  from  the  ordinary  climbing  form  of  Laflnjnts 
odoratus  not  only  in  its  extremely  dwarf  stature  but  also  in 
color  of  foliage,  length  of  internodes,  size  and  arrangement 
of  flowers,  time  of  anthesis,  fertility  and  viability.  Yet  it  is 
certain  that  the  variety  differs  from  the  species  in  a  single 
genetic  factor.  Probably  this  is  as  striking  a  case  as  has 
been  reported  previously,  yet  in  such  a  conspicuous  character 
as  leaf-shape  the  dwarf  variety  very  closely  resembles  the  species 
type.  Now  the  oak-like  walnut  differs  from  the  species  type  in 
every  gross  external  feature — shape  of  leaves,  color  of  foliage, 
color  of  bark,  habit  of  growth,  structure  of  inflorescence,  struc- 
ture of  flowers,  size  and  structure  of  fruits,  as  well  as  in  fertility 
and  viability.  Therefore,  if  tests  that  are  now  being  made 
confirm  our  inference  that  quercina  differs  from  the  species  in 
a  single  genetic  factor,  it  will  be  a  most  striking  example  of 
the    manifold    effects    of    a    single    genetic    factor.      Further- 


2  Morgan,  T.  H.,  Mechanism  of  Mendelian  Heredity,  p.  209ff.,  1915. 


1916]  Babcock:  Studies  in  Juglans,  III  73 

more,  the  demonstration  of  such  a  genetic  relation  between 
quercina  and  californica  must  be  accepted  as  ample  proof  that 
the   first   quercina   individual,  at  least,   originated  by  mutation. 

Since  the  mutant  factor  is  recessive  to  its  normal  allelomorph, 
it  is  highly  probable  that  californica  trees  which  are  known  to 
produce  quercina  seedlings  are  not  to  be  considered  as  mutating 
individuals.  Such  a  tree  is  ./.  californica,  "Garden  Grove  No. 
16",  which  was  referred  to  in  the  preceding  number  of  this 
series.  This  tree  may  he  either  the  result  of  a  mutation  in  on*1 
of  the  gametes  that  produced  it.  in  which  case  it  would,  of 
course,  lie  heterozygous,  or  it  may  he  a  heterozygote  produced 
by  hybridization  between  quercina  and  californica.  The  same 
is  time  of  the  other  two  californica  trees  known  to  have  produced 
quercina.  But  the  genetic  relation  between  the  variety  and  the 
species  shows  that  the  first  production  of  quercina  at  least  must 
have  been  caused  by  a  mutation  in  one  genetic  factor  and  that 
this  change  occurred  in  all  probability  in  a  germ  cell  of  the 
grandparent  of  the  first  quercina  tree. 

A  question  arises  as  to  the  interpretation  of  the  test  of 
the  particular  californica  tree.  Garden  Grove,  No.  16,  reported 
in  the  preceding  paper.  In  1913  the  unguarded  seed  from  this 
tree  produced  about  5  per  cent  of  quercina  seedlings.  The  fact 
that  the  seed  was  not  self-pollinated  under  control  and  so  may 
have  been  crossed  with  nearby  trees  may  serve  as  an  explanation 
of  this  result.  However,  another  explanation  is  indicated.  This 
tree  is  very  late  in  developing  its  pistillate  flowers,  the  stigmas 
becoming  conspicuous  after  most  other  trees  have  shed  their 
pollen  and  after  this  tree  has  shed  much  of  its  own  pollen. 
Xow  if  only  a  portion  of  its  pistillate  flowers  are  self-pollinated 
the  remainder  probably  develop  apogamously.  That  would 
account  for  fewer  qut  rcina  seedlings  than  would  be  expected 
from  self-pollinated  seeds  in  case  this  tree  is  heterozygous  for 
the  quercina  factor.  For  only  one-fourth  of  the  self-pollinated 
nuts  would  produce  quercina  seedlings,  whereas  all  apogamous 
seeds  would  produce  californica  individuals.  Presumably  all  such 
apogamic  plants  would  contain  the  diploid  number  of  chromo- 
somes. Hence  they  would  be  heterozygous  like  their  parent  and 
for  this  reason  they  would  be  californica  in  type. 


74  University  of  California  Publications  in  Agricutlural  Sciences    [Vol.  2 

There  is  also  the  remote  possibility  that  unfertilized  pistillate 
flowers  might  develop  parthenogenetieally,  the  egg-nucleus, 
containing  the  haploid  number  of  chromosomes,  developing 
spontaneously  into  an  embryo.  In  order  that  such  seeds  should 
produce  only  calif  ornica  individuals  it  would  be  necessary  that 
a  single  dose  of  the  quercina  factor  could  not  condition  quercina 
development  even  in  plants  having  the  reduced  number  of 
chromosomes.  This  is  at  variance  with  the  concept  that  Men- 
delian  reaction  systems  depend  upon  proportional  chemical 
relations  such  that  one  dose  of  a  recessive  factor  would  play 
the  same  role  in  an  individual  having  a  haploid  system  as  two 
doses  of  the  same  factor  play  in  an  individual  having  a  diploid 
system.  Therefore,  the  former  is  the  more  reasonable  inter- 
pretation. 

(2)   A  PARALLEL  MUTATION  IN  JUGLA.XS  IlfXHSII 
(JEPSON)   SARGENT 

In  November.  1914,  through  the  courtesy  of  Farm  Adviser 
F.  F.  Lyons,  my  attention  was  called  to  a  nursery  at  Modesto, 
California,  where  there  were  several  thousand  one-year-old  seed- 
ling walnuts.  Here  and  there  among  the  typical  black  walnuts 
I  found  a  number  of  plants  (fifty  or  more)  that  closely  resembled 
./.  californica  var.  quercina  except  that  they  were  taller  than 
qui  rcina  seedlings  of  the  same  age  and  the  leaves  appeared 
somewhat  larger.  Through  the  kindness  of  the  owner,  George  F. 
Covell,  seven  of  these  seedlings  are  now  growing  on  the  campus 
of  the  University  of  California.  These  seven  and  several  that 
were  examined  at  the  nursery  were  found  to  have  come  from 
typical  nuts  of  J.  Jiiiirfsii,  the  northern  California  black  walnut. 
The  trees  that  produced  the  nuts  which  Covell  planted  in  bis 
nursery  are  also  typical  of  J.  hindsii,  but  as  they  had  been  grafted 
to  commercial  varieties  I  was  unable  to  secure  seeds  from  them. 
However  these  grafted  trees  are  seedlings  from  four  large  north- 
ern black  trees  growing  near  Lodi,  California.  Several  hundred 
nuts  from  each  of  these  trees  have  been  germinated  and  only 
seedlings  typical  of  J.  hindsii  have  been  secured.  If  any  one  of 
these  trees  is  repeating  the  mutation  there  is  no  evidence  of  it  in 


1916]  Babcoch:  Studies  in  Juglans,  III  75 

the  immediate  progeny.  This  is  what  would  be  expected  if  the 
new  variety  has  the  same  genetic  relation  to  J.  hindsii  as  quercina 
has  to  J.  calif  or  nica. 

In  an  earlier  paper3  I  proposed  to  designate  quercina  as  J. 
californica  mut.  quercina  and  the  quercina-like  form  of  hindsii 
as  J.  californica  var.  hindsii  mut.  quercina.  However,  the  recog- 
nition of  hindsii  as  a  species4  simplifies  the  problem  and  makes  it 
desirable  to  describe  the  new  mutant  from  hindsii  as  a  variety  of 
that  species  and  to  retain  quercina  as  a  variety  of  californica. 
The  following  description  is  based  upon  material  gathered  from 
several  of  the  seedlings  in  Covell's  nursery  in  1914.  The  seven 
seedlings  growing  on  the  campus  of  the  University  of  California 
are  cited  as  cotypes.  It  should  be  noted  that  the  variety  name 
has  been  chosen  for  the  express  purpose  of  emphasizing  the  fact 
that  the  new  variety  resembles  quercina  in  leaf  characters. 


New  Variety 
Juglans  hindsii  var.  quercinifolia  Babcock 

Tree.  Bark  and  leaves  strongly  walnut-scented.  Pits  in 
plates.  Twigs,  bud  scales,  and  young  leaves  granular  pubescent. 
Buds  few-scaled  axillary  or  superposed.  Leaves  1  to  31/2  inches 
long,  alternate,  exstipulate,  mostly  compound  with  three  leaflets ; 
terminal  leaflet  1%  to  2  times  as  long  as  lateral  leaflets  and 
ranging  from  %  to  21/i  inches  in  length,  in  form  ovate  or 
elliptical,  obtuse  or  truncate  at  the  apex,  margin  irregularly 
crenate  or  serrate ;  lateral  leaflets  mostly  opposite  and  sessile, 
sometimes  one  or  both  lacking,  occasionally  one  or  two  extra  ones 
present ;  petiole  equal  to  or  shorter  than  lateral  leaflets ;  very 
rarely  with  unifoliolate  leaves.      (Cf.  plate  20,  fig.  1.) 

Nursery  of  George  F.  Covell,  Modesto,  Cal.,  Nov.,  1914,  Univ. 
of  Calif.  Herb.  no.  189541.  Cotypes  on  campus  of  the  Univ.  of 
Calif.     (Cf.  Div.  of  Genetics  nos.  755a  to  755gr.) 

Plate  20,  fig.  1  shows  a  specimen  of  quercinifolia  which  was 

supplied  by  Covell  in  1915.  A  typical  quercina  seedling  is  shown 
in  plate  20,  fig.  3.  The  relative  size  of  these  two  seedlings  is  of 
no  significance  as  they  were  not  of  the  same  age.     In  order  to 


s  Babcock,  E.  B.,  Walnut  Mutant  Investigations,  Proc.  Nat.  Acad., 
vol.  1,  p.  535,  Oct.,  1915. 

•ijepson,  W.  L.,  in  Smith,  K.  E.,  Bniv.  Calif.  Agr.  Exp.  Sta.  Bull.  203, 
p.  27  (1909").  Juglans  californica  Wats.  var.  hindsii  Jepson  in  Bull.  So. 
Cal.  Acad.  Sci.,  vol.  7,  p.  23  (1908).         " 


7(>  University  of  California  Publication*  in  Agricutlural  Sciences    [Vol.  2 

emphasize  the  fact  that  hindsii  is  distinct  from  calif arnica  even 
in  the  young  seedling  stage,  a  typical  seedling  of  calif ornica 
and  one  of  hindsii  are  shown  in  plate  21.  figures  5  and  G.  The 
differences  between  the  nuts  of  the  two  species  are  clearly  shown. 
The  mature  trees  of  the  two  species  are  also  strikingly  distinct, 
calif  ornica  being  always  low  and  shrub-like  in  habit  while  hindsii 
is  tall  and  arboreous  in  form. 

These  parallel  mutations  in  two  distinct  species  may  appear 
as  degressive  rather  than  regressive  variations  or.  in  other  words, 
as  cases  of  reversion  to  a  common  ancestral  form.  If  both  quer- 
cina  and  quercinifolia  resulted  from  a  change  in  one  genetic 
factor,  as  seems  likely,  and  both  represent  a  common  ancestral 
form,  then  it  would  follow  that  both  calif  arnica  and  hindsii 
sprang  fully  formed  from  their  common  ancestor  by  mutation. 
Yet  both  quercina  and  quercinifolia  show  reduction  in  morpho- 
logical characters  and  quercina  individuals  exhibit  low  fertility. 
These  symptoms  would  indicate  that  the  mutation  is  regressive 
rather  than  degressive.  However,  the  fact  that  any  walnut  varie- 
ties originate  by  mutation  is  of  significance  for  the  student  of 
evolution,  because  the  Juglandacae  are  generally  considered  as 
one  of  the  older  and  more  stable  groups  of  angiosperms.  They 
are  not  supposed  to  be  undergoing  changes  similar  to  changes 
that  give  rise  to  new  types  in  the  younger,  less  stable  groups. 
That  the  origin  of  these  two  unique  walnuts,  or  of  quercina  at 
least,  cannot  be  explained  on  the  basis  of  hybridization  is  now 
fully  proved.  Evidently  quercina  sprang  from  calif  ornica  rather 
than  calif  ornica  from  quercina,  and  il  arose  as  a  result  of  a 
change  in  a  single  genetic  factor,  i.e..  of  mutation  in  the  strict 

sense. 

Transmitted  May  31,   1916. 


PLATE   20 

Juglans   hindsii   var.   quercinifolia  Babcock 

Fig.   1.     Specimen    from   Covell's   nursery,    1915.      Note    typical    hindsii 
nut,  the  husk  removed  to  show  the  smooth  surface,     x  A. 

Fig.  2.     Halves  of  typical  hindsii  nut.     x  i. 

J.  calif  ornica  var.  qu&rcina  Babcock 

Fig.  3.     Seedling   of  J.   calif  ornica,   "Garden   Grove   No.    16."     Note 
typical  calif  ornica  nut.     x  1. 

Fig.  4.     Halves  of  typical  californica  nut.     x  J. 


[7*1 


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PLATE   21 

Juglans  calif ornica  Watson 
Fig.  5.     Typical  seedling,     x  J. 

J.  hindsii  (Jepson)  Sargent 
Fig.  6.     Typical  seedling,     x  J. 


[SO] 


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